Captain Irongron, an arrogant, bullying, bloodthirsty robber baron is complaining to his faithful lieutenant Bloodaxe about the pitiful state of their supplies. Bloodaxe slyly mentions that there neighbour, Sir Edward of Wessex, stores are well stocked, to which Irongron suggests that they “relieve” him of some of his bounty. Their banter it broken up by what they thinks is a falling star. Irongron wants to set out for it immediately, but his superstitious men are afraid to go out while its still dark, for fear of what supernatural forces might be out there. Bloodaxe stops his master from carving up the men with his battle-axe for their insolence and convinces Irongron to wait an hour till dawn. Irongron orders for wine so they can drink a toast to “Irongron’s Star”.

An hour later Irongron, Bloodaxe and some of his men ride out to find the fallen star. The “star” turns out to be a spherical spacecraft. An armour clad humanoid being emerges from the ship. When Irongron challenges the “star warrior”, it knocks the sword from his hand with a force lance. Bloodaxe tries to convince his captain to flee thinking this is devil’s work but Irongron doesn’t listen, he wants to know what this creature is. The being introduces itself as Commander Linx of the 5th Sontaran Battle Group. Bloodaxe thinks that Linx is a Saracen sorcerer. Linx then plants a flag claiming the planet and its satellites in the name of the Sontaran Empire.

Back at Irongron’s castle Linx is surrounded by a group of nervous pike men and bowmen, that the Sontaran ignores. Irongron brags about how he took the castle by force and killed the original inhabitants. Then boast that his enemies can do nothing because the king has laid tribute and taken their troops to fight in “the wars”. When Linx asks what he’ll do when they return, Irongron gets vague. Linx makes a bargain with Irongron: in return for shelter to complete repairs to his ship, he will give the robber baron magic weapons. While Irongron contemplates becoming King, Linx asks if he has men who work with metal. Unfortunately an armourer and a forger are not what he needs, so he has to find people who have.

In the twentieth century, the Doctor and the Brigadier arrive at a top secret scientific research complex to investigate the disappearance of several scientists and equipment. The Brigadier’s plan is to keep all the scientists at the establishment to keep an eye on them.

Linx has kidnapped the scientists and he has hypnotized them into making repairs on his ship. At the same time he is overseeing the construction of breech-loading guns for Irongron. When Bloodaxe comes to fetch him to Irongron, Linx dismisses him and grumbles about needing their aide.

When Bloodaxe relays this message, Irongron is equally annoyed. Clearly the alliance is not working out. The men are afraid of Linx and his workshop, while Irongron is impatient for the new weapons. He shows Bloodaxe the first of the new weapons and demonstrates it by shooting at an apple on top of a fireplace. He misses the apple by a few inches. Bloodaxe complains about the noise while Irongron vows to master the weapons aim.

Back at the research center, the Doctor meets the babbling, bespectacled Professor Rubeish. The professor complains about being shut up in the barracks, but apparently find a silver lining in the fact that he doesn’t have to see his wife and family! When the Doctor gives his name as John Smith, Professor Rubeish introduces him to Miss Lavinia Smith. When the professor inquires about the TARDIS, the Doctor simply states it’s where he keeps his equipment. The Doctor quickly realizes that this Miss Smith is far too young to be the famous virologist. The girl explains that she is actually Lavinia Smith’s niece, Sarah Jane, a journalist who took her aunt’s place in hopes of getting a good story. The Doctor agrees not to give her away to the UNIT personnel provided she makes the coffee. Before the liberated Sarah can fully explode at the sexist treatment, the Doctor chides Professor Rubeish for writing on the TARDIS. Then, the Time Lord enters the TARDIS for the purpose of making himself a cup of coffee.

At Wessex castle, Lady Eleanor is demanding that her husband, Sir Edward, do something about Irongron. Sir Edward, an elderly, soft-spoken man, meekly explains that theirs little he can do since the king took away his troops. Lady Eleanor argues that Irongron has a small force and they have Hal the Archer and a few men-at-arms. To show he hasn’t been idle, Sir Edward confesses he has sent letters to all their neighbours in an attempt to join their forces and get rid of Irongron once and for all. This placates Lady Eleanor.

Unfortunately, Irongron’s men capture Sir Edward’s squire, Eric. Fortunately for the aging nobleman, neither Irongron nor Bloodaxe can read, but the robber baron guesses correctly that it is a message for Lord Salisbury, requesting for support in defeating Irongron. But no matter how much he threatens and intimidates the squire, Eric won’t confirm Irongron’s suspicions. Irongron has Eric “taken below” to “loosen his tongue”

Meanwhile Sir Edward is justly worried about Eric’s failure to return, despite Lady Eleanor’s soothing assurances. The couple discusses Irongron’s morning routine, how he walks his battlements every mourning. Then Lady Eleanor asks if Irongron is high enough to escape an arrow.

Irongron summons Linx to get information from Sir Edward’s squire (Linx comes, more than likely to stop the constant interruptions). When Irongron asks about Linx’s space armour, Linx simply states that it conceals that fact he is not human. Linx becomes excited at the prospect of war but Irongron doesn’t understand the commander’s talk of space travel. The tension between the two flares up when Linx’s privacy to continue his work and Irongron’s promised weapons. Linx reassures him that as long as Irongron upholds his end of the bargain, so will he. This calms things between them, but Linx seems offended when Irongron states they need each other.

The Doctor is working on his “alarm-clock” when Professor Rubeish pesters him about Miss Smith’s identity. While speaking with Sir Maxwell Dingle he learned that Lavinia Smith is in America, but the Doctor already knows this. The professor wonders if Miss Smith is a spy and what they should do about it. He then tells the Doctor that she tried to convince him that the Doctor was a spy. Sarah then enters and asks if she is on the right floor. The professor bids brusque goodnight and goes to bed. The Doctor explains to an inquisitive Sarah that he is working on a rhondium sensor that will wake him up when it detects delta particles. When Sarah retreats to her cubicle, Professor Rubeish emerges from his cubicle and asks if they should tell the Brigadier about Sarah Jane. The Doctor half-jokingly comments that they can decide what to do about her in the morning - if they’re all still here.

Despite Bloodaxe’s best efforts, Eric has not revealed anything about Sir Edward’s letter. Irongron turns him over to Linx, who uses his lance to unlock the squire’s mind. Irongron is a little disappointed that all Linx did was hypnotize the squire, but questions him anyway. The hapless squire can’t help but answer, revealing the weak state of Sir Edward’s forces and his plan to gather a force against the robber baron. When Linx makes to leave, Irongron demands that he stay. But Linx leaves anyway, causing Irongron to start ranting about the Sontaran’s insolence and what he’s going to do about it.

The rondium sensor detects delta particles, waking the sleeping Doctor. After checking to make sure Professor Rubeish is still here, the Doctor rechecks his equipment. Sarah Jane exits her room and wants to know what’s happening, but the Doctor puts her off. There’s a loud crash from Rubeish’s room and when the Doctor and Sarah investigate, the professor has disappeared!

The Doctor goes out into the hall to investigate and discovers a ghostly figure. UNIT soldiers shoot at the apparition, then it disappears.

Sarah asks what the shooting was, but the Doctor continues to put her off. The Brigadier arrives to make sure everyone is still present, to discover Rubeish is missing. While the Doctor and Brigadier discuss what has happening to the missing scientist, a suspicious Sarah enters the TARDIS. The Doctor prepares to follow the matter transmitter trail left by the professor’s abductor, the Brigadier protests - there’s no telling where the time traveler will end up. But the Doctor bids a hasty good bye and takes off leaving a flustered Brigadier to explain what has happened to the minister.

Outside Irongron’s castle, Hal the archer prepares his bow, then hears (but doesn’t see) the TARDIS arrive.

The Doctor tries not to show his surprise at arriving on target, then sets off to find the source of the matter transmitter. Seconds later a bemused Sarah exits the police box, and sets off to find a telephone.

Irongron walks his battlements, followed by his faithful lieutenant. They discuss how easy it would be to crush Sir Edward’s forces if they could just get past his walls.

Hal pulls back his arrow, but his distracted by Sarah, throwing off his aim.

The arrow thuds into a door behind Irongron. Acting quickly Bloodaxe orders the men to get after him.

Seeing all the men in period costume, Sarah thinks it’s some sort of pageant. So she sees no harm in approaching them to ask about a telephone. So you can imagine her surprise when one of the men grabs Sarah and drags her into the castle.

The Doctor has observed all of this, and is understandably surprised to see the plucky young journalist.

Linx quickly puts his helmet back on when he hears Irongron’s men approaching with the captured Hal. The Doctor is also forced to find a new hiding place.

Bloodaxe brings Sarah to Irongron. Still thinking she’s in the twentieth century, Sarah demands to know what they think they’re doing dragging her through the castle then threatens to go to the police and report their actions. Irongron is intrigued by this headstrong fiery girl, but turns his attention to the arriving Hal. The archer confesses that it wasn’t Sir Edward who sent him, but Lady Eleanor. Irongron sends him away to be dealt with. Irongron and Bloodaxe joke about Hal’s fate. When Sarah can’t get what she feels is a straight answer she tries to deduce where she is: it’s too realistic to be a village pageant and there are no cameras for a movie set, so it must be a tourist attraction. Irongron and Bloodaxe are now convinced Sarah is hopelessly mad. Linx arrives to show his latest invention, and Bloodaxe asks his captain’s permission to leave and deal with the prisoner. Sarah at first distracts Linx. The Sontarans are a clone species, neither male nor female, they are hatched at each muster parade. He’s ready to pass her off as simply the secondary part of the human reproductive cycle until he notices that her clothing is machine woven. Linx hypnotizes Sarah to reveal how she got here. Considering the twentieth century has no knowledge of time technology, Linx becomes worried. Irongron pesters Linx about the weapon he was going to show him and the commander brings in a towering robot dressed in medieval armour. Irongron now muses that with an army of these he could take the world, something Linx finds amusing. Meanwhile, Sarah manages to shake off the hypnosis and slips away unnoticed. Linx demonstrates how to use the robot’s control box.

The Doctor meets up with Sarah in the corridor, but as soon as she sees him, the female journalist turns and flees in the opposite direction. Before the Doctor can go after her, two of Irongron’s men drag Hal by, forcing the Doctor to take cover.

Outside, Hal is placed on a chopping block and just as Bloodaxe prepares to relieve the young archer of his head, Irongron intervenes. The robber baron offers Hal a chance to fight for his life. If he can defeat “Irongron’s Champion” (the robot) he can go free. Bloodaxe protests that it isn’t fair combat as at this close range the arrows can pierce the armours weak points. A confidant Hal puts an arrow in his opponents chest - but before an astonished group and a laughing Irongron, the iron man continues moving! Hal puts another arrow in the knight’s chest to no effect.

Riveted by the scene in the courtyard, no one sees the Doctor appear and pick up a crossbow.

Just as the robo-knight is preparing to deliver a killing blow, the Doctor shoots the control box from Irongron’s hand. The robot goes berserk and starts advancing menacingly at Irongron. Bloodaxe tosses him an axe to defend himself, but despite chopping its head off it still comes. The robot falls on its side but continues wriggling on the ground. An angry Irongron vows to have a word with Linx about this and leaves as the men gather around squirming the robot, laughing.

In the confusion, Hal as managed to escape with Sarah.

Irongron kicks his way into Linx’s lair and gets a look at his benefactor’s face. For the first time he shows uneasiness around the star warrior. The robber baron quickly recovers from his shock and relates recent events. Linx muses that the hand control is probably a weakness in itself then promises to build a robot that will obey the chieftain's voice. They then leave to deactivate the now useless automaton.

The Doctor sneaks into Linx’s laboratory through a vent, then explores the lab. He comes across a virtually blind Rubeish, who happens to be the only one in the lab not hypnotized. Although the professor claims this is because he’s too strong minded, the Doctor thinks its because Linx is using an ocular device. Rubeish is fascinated when the Doctor tells him he’s been taken back in time, and refuses to leave when the Doctor tries to take him away. As the Doctor tries to convince him of the danger, Linx bursts in and shoots the Doctor.

Hal and Sarah have meanwhile made it back to Sir Edward’s castle. The nobles find her clothes and speech strange but are willing to trust her when Hal vouches for her. After informing then of what is going on at Irongron’s castle, Sarah explains things as best she can. Sarah believes the Doctor is the one kidnapping the scientists and helping Irongron. Frustrated with Sir Edward’s defeatist attitude, she proposes a raid to capture the Doctor. Hal volunteers to go as well and the aged nobleman concedes.

The Doctor has been able to resist Linx’s influence, but was stunned in the assault. The Doctor learns that a Rutan squadron shot down Linx while on a reconnaissance mission. Linx learns that the Doctor is from Gallifrey - he is a Time Lord. The two them get into a verbal sparring match about each other’s cultural good and bad points. Linx has particular disdain for the “Earth primitives”. The Doctor tries bargaining with Linx, but the commander isn’t interested. Instead he hooks the Doctor up to a machine to monitor the energy output programmer. The Doctor again tries to talk Linx out of giving Irongron the guns, only to receive an electric shock for his troubles. After the commander leaves, the Doctor tries to remove the headset only to receive more shocks.

Sarah, Hal and two men-at-arms manage to sneak into Irongron’s castle after knocking out a dozing guard. Hal doesn’t think this is job for women, but Sarah points out that she’s the only one who knows what the Doctor looks like.

Irongron admires his knew weapons and reveals his plans to Linx and Bloodaxe to attack Wessex castle at dawn, not knowing that Sarah and Hal are listening in at the window.

Meanwhile Rubeish has released the Doctor from Linx’s machine. The Doctor thanks the professor then sets off to find Miss Smith.

No sooner does he leave Linx’s lab, he runs straight into Irongron and Bloodaxe. The Doctor uses his Venusian Acid to escape them and dash outside.

For the second time in so many days, Irongron has something shot out of his hand. This time its Hal shooting the axe out of the robber baron’s hand. The distraction allows the Doctor to escape up a turret. When Irongron and his men give chase, the Doctor starts a fire blocking their pursuit. The Doctor thanks Miss Smith for the rescue, only to have Sarah inform him curtly that this is a capture and his lead away by the men at arms.

Linx returns to his lab to find the Doctor gone. Linx leaves all the time being watched by a hiding Professor Rubeish. When Linx is gone, Rubeish continues working on a makeshift eyeglass.

Irongron rants about what he’s going to do to the Doctor when he sees him again and Bloodaxe points out he’s with Sir Edward now and tomorrow his captain will get his chance. Bloodaxe rises nervously when Linx arrives to demand that Irongron have his men search for the Doctor. Irongron isn’t interest in the fate of one of Linx’s “way faced ninnies”; he’s letting his men rest before the attack at Sir Edward’s. Just as it looks like the argument is going to get violent, Bloodaxe remembers that somebody called out Doctor (“a longshanks fellow with a mighty nose”)while they were chasing him. This news does not sit well with Linx.

The Doctor meanwhile is surprised (and slightly amused) that Sarah is already on good terms with the local nobility. Sarah on the other hand is far from amused. The Doctor is appalled to learn she thinks he is kidnapping the scientists and is using them to help Irongron. Under the watchful eye of Hal, he explains he works for UNIT and was helping them in the investigation of the missing scientists, and that it is Linx who is responsible. Sarah remembers a strange looking knight and admits to the newly arrived Sir Edward and Lady Eleanor that she made a mistake. The Doctor can’t help but tease Sarah about this, to which she replies he is probably just trying to save his life. Sir Edward and Lady Eleanor are wary of the Doctor, knowing that “wizards are an untrustworthy breed”. The Doctor assures them that he is not their enemy and offers his services to stop Linx and Irongron (especially since Sir Edward has given the options of helping them or being executed). Hal suddenly remembers that Irongron will be marching on Wessex castle within the hour. The Doctor tells Sir Edward he need not worry, as he is sure that he can convince Irongron that they have a full garrison.

As Irongron and Bloodaxe prepare for battle, Linx asks to go with them. Irongron finds this amusing and instructs Bloodaxe to find Linx a horse.

Everyone at Wessex castle is scrambling to prepare for his arrival. The Doctor’s plan is to line the battlements with dummies dressed up as soldiers. Lady Eleanor has the serving wenches sewing the clothes while Sir Edward paints the faces. The Doctor meanwhile is concocting a special stink bomb with a few smoke and bangs for good measure. Sarah gives the Doctor an update on their progress. The two start talking and a mutual friendship blossoms. The Doctor admits to a shocked Sarah that he isn’t human and refers to the Time Lords as “galactic ticket inspectors”. Their conversation is interrupted by the sounds of trumpets indicating the arrival of their enemy.

At first Irongron is convinced by the illusion and is ready to return to his castle, but resumes his campaign when Linx tells him to use the rifles.

Atop the battlements, Sir Edward’s men hide between the exposed dummies. The Doctor arrives with his secret weapon with Sarah in tow.

When Irongron first uses the rifles he misses his target completely, but when Linx uses a rifle he hits it dead on revealing the Doctors ruse. Irongron orders his men to bring the scaling ladders.

While the rogues begin scaling the walls, the Doctor almost casually throws the bombs over the side of the castle wall. The stench along with the small (but harmless explosions) scatters the men. Realizing the battle is lost, Irongron angrily orders his men to retreat.

Back at his castle, Irongron is not I a good mood. He chews his men out for scaring so easily, while they try and wash the stench from their senses. Bloodaxe makes lame excuses about black magic on the Doctor’s part, but eventually manages to calm Irongron down enough for the robber baron to send his men away to rest. As they leave, Linx enters and the men quickly get out of his way. The tension between Linx and Irongron is boiling over. When Irongron threatens him, Linx casually swats the big man aside and exits announcing that he’ll be grateful when he leaves this miserable planet.

Meanwhile, the Doctor, Sarah, Hal, Sir Edward and Lady Eleanor are having a celebratory dinner. Sarah is a little confused about some of the dining customs of the Middle Ages, but is obviously enjoying herself. Sir Edward’s good humor is doused when the Doctor points out that Irongron is bound to attack again and the next time he won’t be so easily fooled. But the Doctor does have another plan … he intends to capture Irongron’s castle. He hands Lady Eleanor a list of herbs. The lady believes he intends to make a magic potion, to which the Doctor simply smiles.

Irongron is ranting again, this time about what he should have done to Linx to which Bloodaxe replies why he didn’t. Irongron covers by explaining that he still needs Linx to give him weapons from the stars. Bloodaxe compliments his master by saying he has a towering intelligence, Irongron seems to think it’s an insult.

The Doctor and Sarah gain access to Irongron’s castle by posing as friars coming to beg ahms of “the good Captain Irongron”. After letting them through, the guards’ joke that it looks like the church is about to get two new martyrs.

Once inside, they go to Linx’s workshop and meet up with Professor Rubeish. The professor shows the Doctor that the scientists are starting to drop due to starvation.

Linx curtly drops a crate of rifles and projectiles on the table Irongron and Bloodaxe are brooding at. Linx tells them he will finish the repairs to the fighting robot if there’s time before he leaves. Irongron scoffs at the idea. How does Linx plan to get his ship out of the castle? This doesn’t concern Linx. He simply tells Irongron to not try and stop him.

The blast is cut short when Sarah attacks Linx. They struggle briefly before the commander throws the girl aside. Just as he’s about to kill Sarah, one of the scientists collapses. Linx commands him to get back to work, but a groggy Doctor tells him its pointless. The scientists haven’t had any food or water in days, they can’t go on. All Linx cares about is getting back to the war with the Rutans. Rubeish knocks out Linx by hitting him on the probic vent (a hole on the back of his neck). Sarah leaves to begin the second part of the Doctor’s plan while he and the professor secure Linx. As the Sontarans muscles are more for load bearing than leverage, rope suffices.

In the great hall Irongron inspects the rifles then orders Bloodaxe to fetch Linx

The Doctor and Rubeish finish trying up Linx just as Bloodaxe arrives. The Doctor impersonates Linx and sends a nervous Bloodaxe away. The Doctor leaves Rubeish to de-hypnotize the scientists, while he disguises himself as the robot to stall Irongron.

Sarah meanwhile has made her way to the kitchen, but is almost immediately caught by Meg, the chief serving wench, and accused of being a thief. Sarah overplays her part a bit by trying to bluff her way out of the situation, by acting like a lady. But Meg points out that she’s dressed as a serving girl. Thinking quickly, Sarah relates a sob story about not eating for months. Meg puts her to work.

The Doctor arrives in the great hall disguised as the robot. Irongron wants to see the mettle of this robot and challenges the Doctor. The Doctor tries to talk his way out but Irongron won’t her of it. The two duel. Bloodaxe is impressed. He’s never seen a finer swordsman. Irongron agrees and invites his lieutenant to join him.

Meg runs the kitchen the same way Irongron rules the castle. When Sarah asks about the noise upstairs, Meg puts it off to men’s foolery, then orders Sarah back to work.

The Doctor is holding his own against his two attackers. Irongron wants to see if the iron man can fight just as well with an arrow or two in it then chop its head off if that doesn’t work. The Doctor protests and Irongron wonders why the robot is all of a sudden talking like a “Norman ninny”. He lifts up the visor to discover it’s the Doctor. The Doctor tries to escape but is captured. Irongron decides that as the Doctor is a wizard, he shall die by wizardry.

Meg is getting tied of Sarah’s constant questions. Sarah tries to jump-start the feminist revolution, but the worldly Meg is a product of her time. She knows that as long as there are men, women will never be free. Sarah pours the sleeping draught into the food when Meg’s back is turned.

Rubeish has successfully released the other scientists from Linx’s control and brings them up to speed. He then tells them they must continue to pretend being hypnotized until the Doctor returns. Irongron enters looking for Linx. Even he now seems uneasy around Linx’s workers. He find’s Linx tied up and cuts him loose. When Linx asks where the Doctor is, Irongron replies “dying”.

Irongron has decided to use the Doctor for target practice. His men need practice in the use of their magic weapons. The Doctor’s nimble footwork and the rogues’ bad aim are the only things that save him from the flying projectiles.

Meg enters the kitchen and tells the other women what all the shootings about. Sarah dashes off while Meg complains why they just don’t use a broad sword to kill the Doctor.

The Doctor has managed to avoid getting shot. Linx is impatient to kill the Doctor, so he asks Irongron to give him a weapon. But the robber baron is to busy enjoying himself. Sarah comes to the Doctor’s rescue by swinging a chandelier in his direction allowing him to swing out the door. The Doctor slams the door behind him and bolts it shut. They race through the castle and escape by knocking out the sentries.

They return to Wessex castle to let the sleeping drug take effect. Lady Eleanor is pleased to here the castle will be destroyed by sorcery but the Doctor reminds the others that he still has to get the scientists back home. Hal and Sarah volunteer to go with him.

Meanwhile the repairs to Linx’s spaceship have been completed. He powers up the ship to take off and tells the scientists that their work is finished and they are aloud to rest. Linx leaves to inform Irongron of his departure. Rubeish begins worry where the Doctor is.

The returns to the TARDIS to retrieve what looks like a metal fan.

Sarah and Hal watch as the sentries fall asleep from the potion. The Doctor arrives and they sneak in. they go to Linx laboratory where Professor Rubeish informs him that Linx put everything back in the ship. The Doctor sends Hal to disarm Irongron’s men, then begins to send the scientists back home using Linx’s osmic projector.

Irongron and his chamber guard are having a feast to commemorate tomorrow’s victory, and he laughs at Linx’s announcement that he’s leaving. Shortly after Linx exits, the sleeping potion takes it effect on Irongron and the others at the table.

Linx returns to his workshop, to find the Doctor sending the others back. The Doctor has Rubeish send the others through while he keeps Linx occupied. He uses the metal fan to deflect Linx’s gun blasts. His gun not working, Linx tackles the Doctor in physical combat. The Doctor keeps the Sontaran off balance with his Venusian Aikido.

Hal has meanwhile been disarming Irongron’s sleeping men. But when he starts to disarm Irongron himself, the chieftain comes to and throws Hal across the room knocking him out. Still under the effects of the drug, Irongron staggers to Linx’s lab believing he has bewitched him.

Sarah sends Rubeish back through the osmic projector just as Linx manages to outmuscle the Doctor. Linx picks up his gun and prepares to finish off the Doctor, but Irongron bursts in and attacks Linx. The Sontaran effortlessly kills him and returns to his ship. Full power has been restored!

Hal comes too he wakes Bloodaxe and tells him that the castle is very shortly going to be destroyed by magic, then races back to the lab. Hal’s news sinks in and he rouses the rest of the men to flee the castle.

Sarah has meanwhile been trying to rouse an unconscious Doctor when Hal returns. As the door to Linx’s spacecraft closes, Hal shoots and arrow into Linx’s probic vent, killing him. Linx’s dying action is to press the take off button. The Doctor and company run as fast as they can out of the castle as machinery explodes throughout the lab.

The Doctor, Sarah and Hal dive out of the castle just as it is reduced to rubble.