The Doctor is supposed to be taking Charley to Singapore 1930, but for some reason the TARDIS seems unwilling to complete the journey. Instead, it materialises somewhere in pitch darkness, and doesn’t provide any data on its location. Eagerly anticipating a good mystery, the Doctor sends Charley out to learn what she can about their surroundings, while he fetches torches from inside the TARDIS; however, while exploring she inadvertently knocks over something made of glass, shattering it. The Doctor emerges with a torch to find that the wall next to Charley is now dripping with what seems to be blood... but upon closer examination, he’s relieved to find that rather than severing an artery, she’s just knocked over a jar of raspberry jam. They soon determine that they’re in the rather well-stocked larder of an Edwardian family manor, and set off to explore further.

Elsewhere, scullery maid Edith Thompson scrubs the pots and pans, and sings Hark the Herald Angels Sing, humming the bits she can’t remember. The butler, Mr Shaughnessy, interrupts her caterwauling and angrily points out the dust which has built up on the table due to her neglect. To prove his point, he writes her name in the dust; to little avail, as she can’t read. Subdued, she returns to work quietly, reminded as always that she is nothing and nobody -- a sentiment shared by the household cook, Mrs Baddeley. Christmas wouldn’t be Christmas without Mrs Baddeley’s famous plum puddings, but she also has to prepare the turkey, and she thus summons Edith from the scullery to help. She’s irritated when Edith protests that she’s been told to work on the scullery, and contemptuous when Edith further demonstrates her general clumsiness and idiocy by burning her hands while trying to pick up the plum pudding. Edith only makes things worse when she wonders aloud why the servants’ plum pudding is smaller than the one for upstairs, even though there are more servants than there are gentry. The butler and the cook are aghast; they are nothing and nobody, and Edith will never fulfill her dreams of becoming a cook if she carries on like that. Shaughnessy leaves to attend to his duties, but Frederick the chauffeur then arrives to speak with Mrs Baddeley. Mrs Baddeley thus sends Edith away; what she and Frederick have to discuss is between them alone...

The Doctor and Charley emerge from the larder into a darkened scullery, which Charley compares to her the one from her own house in 1930. This scullery is larger, but the washing equipment is less advanced, suggesting that this is an earlier time period. The Doctor finds and lights some candles, and returns his anachronistic torches to the TARDIS while Charley remains in the scullery. The washing-up has been abandoned, as indeed the whole house seems to have been -- but when the Doctor returns, he and Charley find that the water in the sink is still warm. The name “Edith Thompson” is written in the dust on the table, but as Charley idly writes her own name beside it, recalling the Edith who once worked for her family, the dust closes up around Charley’s name, erasing it. The Doctor then informs her that the broken jar in the larder has reassembled itself, and Charley realises that her dress is no longer stained. Intrigued, the Doctor and Charley proceed to the kitchen, which also appears dark and abandoned -- and yet contains a turkey and two plum puddings, all prepared for Christmas. Charley has never liked plum pudding that much, as her own cook always made too much of it and Charley once broke a tooth on a thruppeny piece hidden inside. But as Charley idly recalls Christmases past, she hears someone singing Hark the Herald Angels Sing, very faintly, in the background. The Doctor can hear nothing -- and he’s starting to become unnerved.

Frederick the chauffeur arrives in the kitchen to speak with Mrs Baddeley. Mrs Baddeley thus sends Edith away; what she and Frederick have to discuss is between them alone. For a moment, however, Edith pauses, hearing two faint and unfamiliar voices in the kitchen with her... As soon as Edith has gone, Mrs Baddeley lets Frederick know, in no uncertain terms, that she’s disgusted by what he’s been doing with the lady’s maid, Mary. If Mrs Baddeley tells the lady of the house what she’s seen, then Frederick and Mary will be expelled from the house in shame. Frederick tries to offer the cook a bribe, and then tries threatening her; she’s left him with nothing to lose. Mrs Baddeley, furious, kicks him out of her kitchen. Frederick returns to the servants’ common room, where Mary is waiting with a sprig of mistletoe; however, Frederick breaks it off with her, claiming that their past trysts were a mistake. For a moment, Mary suspects that Frederick prefers Edith, but that’s silly -- nobody could possibly love a girl like her. Frederick insists that they have no right to love; they are nothing, and nobody. But Mary won’t let anyone stand in her way -- not Mrs Baddeley, and not even Frederick himself.

The Doctor and Charley enter the servants’ common room, where the fire in the grate is frozen in a moment of Time. They try pulling a Christmas cracker, which snaps back together moments later; it’s as though they can’t affect anything in this frozen moment. To test this theory, the Doctor pulls the cracker again and this time grabs the paper hat from inside before the cracker can reassemble itself. He and Charley can influence the frozen world after all -- and if they’re not careful, it can influence them. Even more disturbing is the joke from within the cracker -- the old chestnut “When is a door not a door” is answered “When it’s a raspberry jam jar.” Time is being manipulated by some intelligent force, which is deliberately mocking the Doctor and Charley...

The Doctor tries tossing his paper hat into the fire, which unfreezes just long enough to burn the hat. Charley then hears the distant caroling again, and when the Doctor burns the cracker and then the tablecloth, the sound gets louder. Only Charley can hear it, and when she follows it to the scullery and tries to communicate with the singer, she hears the sound of a ticking clock -- and is overwhelmed by angry and contemputous voices, shouting the putdowns and rage which Edith has had to suffer through all her life. Charley suddenly finds herself standing next to Edith, who’s surprised, cowed and delighted to find herself speaking with a lady from upstairs. Honoured that Charley is treating her kindly, Edith proudly shows Charley her name in the dust -- but as they watch, Charley’s name appears there as well, where she tried and failed to write it earlier. It’s as though Charley is now a part of Edith’s world -- and Edith suddenly becomes cold and distant, telling Charley that soon she, Edith, will die. Everyone will then forget she ever existed -- but Charley must remember.

The Doctor and Charley find themselves in the lit, living scullery -- but time has run out for Edith Thompson, whose head is submersed in the kitchen sink. The other staff members enter to find the Doctor and Charley trying to revive her, and, oddly, they all greet the Doctor as the chief inspector of Scotland Yard, and Charley as his niece. Shaughnessy announces that Edith must have committed suicide, and when the Doctor points out that she would have passed out and fallen out of the sink before she could have drowned, Mrs Baddeley concludes that she was too stupid to realise that what she was doing was impossible. The Doctor and Charley find this unlikely; thus, they will have to question each member of the staff individually to determine who is the guilty party, as is usually the case in such matters. Until then, the staff return to their duties. Mrs Baddeley is sure to check on her plum puddings first; Christmas wouldn’t be Christmas without them.

Charley recognises the trappings of a classic Agatha Christie mystery, and is disappointed that she and the Doctor haven’t been cast as amateur sleuths. Levity aside, she’s also upset by her failure to save Edith -- but how did the maid know she was going to die? Come to that, how did she have time to scream if she was drowning, and why was she killed at precisely 10:00 in such a contrived manner? The Doctor fears that the intelligence behind the time anomaly is trying to fit him and Charley into set roles within its scenario, but decides to play along for the moment. First, he questions Shaughnessy, who does not mourn Edith’s death, but regrets only the loss of the house’s scullery maid. He knows nothing of the staff’s lives, identifying them only by their roles within the household; beyond that, they are nothing and nobody. He becomes very uncomfortable when questioned about the family upstairs; it’s not his place to discuss his masters. His only purpose is to serve. As for the murder, he claims to suspect Mrs Baddeley, for she has shifty eyes.

Mary is extremely upset when Mrs Baddeley assigns her to finish Edith’s work in the scullery; she’s supposed to be a lady’s maid, and this is quite a fall in her perceived social standing. She departs with bad grace as Charley enters to question Mrs Baddeley; however, rather than answer her questions about Edith’s death, Mrs Baddeley coos over Charley, treating her like a little girl and offering her plum pudding. She becomes quite offended when Charley refuses, and refuses to speak until Charley gives in and tastes the plum pudding. Christmas wouldn’t be Christmas without it -- and it’s always been Charley’s favourite, ever since she was a little girl. Charley begins to act like a little child as well, but realises that something odd is happening to her and regains her senses. Before she leaves, she tries to question the cook about the murder, and Mrs Baddeley claims to suspect Frederick, for he has shifty eyes.

The Doctor questions Frederick, who, oddly, now seems to believe that the Doctor is a famous amateur sleuth -- the same one who solved the mystery of the Seven Dials. This is in fact an Agatha Christie mystery, and although the year is currently 1906, Agatha Christie’s first novel won’t be published until 1920. Also, Frederick claims to drive a Chrysler, which won’t be invented until 1924. Frederick tries to correct himself, but he clearly isn’t sure what the error is. Something is dreadfully wrong here. As for the murder, Frederick claims to suspect Mary, for she has shifty eyes.

Charley tries to question Mary, who seems the most upset -- not because a woman is dead, but because Mary is now being forced to do scullery work. As for Edith’s murder, Mary claims to suspect Edith, for she has shifty eyes; when reminded that Edith is the one who was murdered, however, she claims to suspect Mr Shaughnessy, for he has shifty eyes. Charley suddenly finds herself back in the dark again, with Edith Thompson, who now seems cold and accusatory towards her. Edith is weary of dying, and refuses to tell Charley who killed her; all she will say is that there will be another death soon, and that everyone will then forget that Edith existed. But Charley must remember her -- and she must remember that Edward Grove is alive...

The clock chimes eleven, there is a scream, and Charley finds herself in the kitchen with the body of Mrs Baddeley. The Doctor arrives, and examines the body to find that the cook has been smothered with her own plum pudding. Shaughnessy is extremely upset by the loss of not only another staff member, but the plum pudding as well. Again, the surviving staff members assume that this was a suicide, and the Doctor, puzzled, dismisses them while he and Charley discuss the deaths. Charley tells the Doctor about her encounter with Edith, but he can make no sense of her story or of this latest murder. Who is Edward Grove? The killer can’t be a stranger, for that would break the rules of the genre; and the Doctor is sure that there are rules to what is happening here. Why else would the murders represent the victim’s professions and take place exactly on the hour? It must have taken several minutes for the killer to stuff Mrs Baddeley full of plum pudding, so how could Charley and the Doctor have found the body only seconds after hearing the scream? Did the killer scream to draw attention to the body, and if so, why? Charley then realises that although this death supposedly took place exactly one hour after the first, it certainly didn’t seem as though an hour had passed. The Doctor realises that the being in charge of this game has changed the rules to make Time run faster...

Elsewhere, Mary confronts Frederick, convinced that he murdered Mrs Baddeley in order to keep their secret. However, he claims that he suspected her of being the killer. At any rate, with Mrs Baddeley out of the way they’re free to carry on as before... or so Mary thinks, until Frederick points out that the very idea is ludicrous; a chauffeur, in love with a scullery maid? Mary is taken aback, as she’d thought Edith was the scullery maid -- but Frederick has never heard of Edith Thompson, and neither, Mary realises, has she. Mary has always been the scullery maid, and Frederick could never love her; she is nothing, and nobody. Subdued, Mary returns to work, humming Hark the Herald Angels Sing...

Oddly, the Doctor and Charley are unable to locate any clocks downstairs, even though they can clearly hear a grandfather clock ticking. The Doctor asks Shaughnessy for help, but the butler claims that the staff don’t need to know the time; they need only to obey promptly when given orders. He becomes very uncomfortable when the Doctor asks to borrow his fob watch, and when the Doctor, exasperated, decides to take his investigation upstairs, Shaughnessy apologetically pulls a gun on him and refuses to let him disturb the gentry. While under threat, however, the Doctor asks Shaughnessy for his watch again, and this time Shaughnessy hands it over without objection, thus proving that the force which controls the household can’t concentrate on more than one thing at a time. For now...

For a moment, the Doctor and Charley are back in the darkness, and this time, they can hear the sound of a beating heart. Then they reappear in the scullery, and this time, Edith is lying dead on the floor, having been suffocated by a sink plunger. Once again the staff enter to find the Doctor and Charley over Edith's body, and this time, they greet them immediately as amateur sleuths. Apart from a few minor variations, however, they replay the same sequence of events, first suggesting that Edith committed suicide, and then fretting over the state of Mrs Baddeley’s plum puddings. The Doctor notes another difference -- the name Edward Grove is now written in the dust beneath Edith and Charley’s names, as if the killer is signing his name to a work of art. Disturbed, the Doctor leaves to check a theory, telling Charley to stay with Mrs Baddeley, whom they know will be the next victim.

The Doctor visits the common room, where he orders Mary to open the door so Frederick can take him for a drive. The servants object, reasonably enough; Frederick can’t drive thorugh the blizzard outside, and opening the door would let the cold in. When the Doctor insists, they apologetically threaten to kill him, bound to do as their master has instructed. The Doctor thus returns to his assigned role and questions them about the murder, although he’s starting to doubt that the murder is really important. Mary and Frederick claim to believe that one of them must be the killer, as Mrs Baddeley stood in the way of their love; however, the Doctor points out that Mrs Baddeley hasn’t actually been killed yet. Frederick, confused, wonders whether he’s the one who’s been killed -- or has that yet to happen?

Charley is surprised to realise that Mrs Baddeley has forgotten about Edith’s death already. Once again, the cook offers plum pudding to her dear little Charley, and this time Charley does sense something familiar about the offer. But she still doesn’t understand why Mrs Baddeley claims that Charley was always her only friend. The cook was so upset when Charley died -- but now she’s back from the dead... The darkness returns, as does the sound of the heartbeat and the ticking clock. Edith is still hidden in the dark, weary of all the death and angry that Charley has forgotten her like all the others. Why did she have to die, if Charley is alive after all? Now Edward Grove is alive, and only Charley can stop this...

Charley finds herself back in the kitchen as the clock strikes 11:00, but Mrs Baddeley isn’t the victim this time; there is a scream from the common room, and Charley and Mrs Baddeley rush to investigate to find that Frederick has apparently been run over by his own car. The Doctor saw nothing -- when the chimes struck, the room went dark for a moment and then restarted with Frederick lying dead. Mary weeps for her lost love until Shaughnessy reminds her that she’s a scullery maid; thus, Frederick could never have loved her. Once again, Shaughnessy suggests that Frederick killed himself, and the Doctor begins to wonder why the staff are so insistent that suicide is being committed in this house...

The Doctor and Charley discuss the bizarre nature of the murders; what’s the point of death if the victim returns to life again afterwards? There’s no pleasure being taken in the deaths, and the victims suffer no fear -- in fact, Frederick even seemed to be aware that he was going to die. Charley is deeply upset, especially since she feels that she’s failing Edith, whom she considers a friend. Fearing that the force in charge of the house is trying to incorporate Charley into its reality, the Doctor urges her to resist the false memories, but Charley vows to keep her promise to Edith and returns to the scullery... only to find that Edith’s name has been erased from the dust. Edith speaks to her again, deeply bitter -- why did she die for Charley when Charley has forgotten her like all the others? More letters appear on the table, carved into the wood itself. “Edward Grove is alive” -- and Edith and Charley are responsible.

The Doctor begins to climb the stairs, and Shaughnessy rushes in to hold him at gunpoint again. The Doctor in fact had no intention of going upstairs; he just wanted to force his enemy into direct action, and Shaughnessy is now starting to understand that his behaviour doesn’t make any sense. The Doctor explains that he’s been dulled by repeated cycling through a time loop, just like the rest of the staff, making them ideal for the enemy to manipulate at will. But who is the enemy? Who is Edward Grove? Shaughnessy’s answer confirms the Doctor’s suspicions -- this house is 22 Edward Grove. The house is alive. Mary and Mrs Baddeley arrive, having been ordered to kill the Doctor, but he urges them to resist Edward Grove’s control; they are human beings, worth more than mere architecture. They find that they cannot kill the Doctor yet, as Edward Grove can only act on the stroke of the hour. As Time speeds up, racing towards midnight, the Doctor urges the staff to try describing the masters they serve; if they cannot do so this will prove they have no human masters. But Charley arrives, having fallen under Edward Grove’s spell -- she now believes that she is the daughter of the house and has no idea who the Doctor is. Appalled, the Doctor tries to wake her to a sense of herself, as the hands of the clock race towards midnight...

As midnight strikes, time loops back on itself, sending the Doctor and Charley to the beginning of the cycle -- with Edith lying dead in the scullery, bludgeoned to death with her own broom. Charley has recovered, but the staff remain part of the loop and rush through their prior moves with indecent haste. The Doctor realises that Edith’s death must be the key to this. Theories suggest that “ghosts” are in fact traumatic emotional impulses recorded in the very fabric of a haunted house; perhaps this house has been caught in a time loop, replaying the same death over and over so many times that it’s developed sentience. Now it requires death to survive, and it is manipulating the time loop to feed itself, growing stronger each time somebody dies...

The Doctor opens the larder door to reveal the TARDIS standing inside -- but when Charley opens the TARDIS door she sees yet another scullery inside the TARDIS. The time loop is also an infinite spatial loop, and the Doctor and Charley are doomed to go around in circles within it for all eternity. Shaughnessy returns and greets them warmly, as the staff have now accepted their fate -- they will serve Edward Grove for the rest of their lives and beyond. Before the Doctor can protest, Charley vanishes, sent back into the darkness; however, Shaughnessy assures the Doctor that she will not be harmed. She is the means of Edward Grove’s birth. Time speeds up to reach 11:00, and then slows down, extending the chimes of the clock and allowing Edward Grove to possess Shaughnessy and speak directly to the Doctor for the first time...

Charley is in the darkness again, and Edith remains hidden in the shadows for fear that Charley will not remember her. Charley once again promises to help her friend, and thus, Edith emerges from the darkness -- and Charley recognises her as the cook from the Pollard home in Hampshire. In 1906, she was still a scullery maid, but by 1930 she’d become a cook, the same one who made plum pudding for her dear little Charley. Charley was the only one who ever showed Edith any kindness in her life; everyone always told her she was nothing and nobody, even the chauffeur who seduced her in 1926 and then pretended that it had never happened. It wasn’t Frederick who did so, but it might as well have been; the humiliations all blur together. Now Edward Grove is playing out her life in miniature, condensed into a two-hour time loop... and all because Edith died for Charley. When they found Charley’s diary in the wreckage of the R101, the household went into mourning -- but Edith, merely a servant, wasn’t allowed time to mourn. On Christmas Eve, nobody wanted her plum pudding, and she knew that the only person who had ever shown her kindness was gone forever... and thus, that night, she slit her own wrists in the kitchen. Nobody cared to investigate the scream, and it took her a long time to die. But if Charley’s alive after all, then what was the point? Charley, deeply upset, realises that she can remember the flames surrounding her; she can remember the sick feeling she got as she knew that she was going to die. She did die on the R101, and that means that Edith died too... and Charley can no longer remember the Doctor.

The Doctor and Edward Grove are also starting to understand what’s happened. Though Edward Grove derives power from the time loop, it only feels fully alive when it can hear time passing -- when the clock chimes the hour. The Doctor, disgusted by the pettiness of Edward Grove’s ambitions, accuses it ot parasitically feeding off its servants’ lives, but isn’t that just what their human masters always did? The servants are nothing and nobody, and there’s nothing petty about wanting to live, even if only for a few seconds of every hour. Edward Grove no longer wants the Doctor dead -- for he knows that the Doctor is responsible for his existence. Everything that occurs in this house is an echo of a larger event, the death of Edith Thompson in 1930 -- a suicide which became impossible when the Doctor and Charley arrived in 1906. It’s not the death which gives Edward Grove life, it’s the paradox.

Realising that Edward Grove is maturing, the Doctor tries to speak sense to it; the particular time loop is a freak, unnatural occurrence, and Edward Grove can only ever have an echo of true life, a few brief seconds of full existence every hour. Even the house itself understands that its servants are far more complex than itself, but it shies away from the next logical step; for freeing them from this infinite loop and giving them the full lives they deserve would mean its own death. Having tasted life, it refuses to give up what little it has; instead, it has a new idea. Rather than flicker into full awareness for a few seconds in every hour, it will crush the time loop down into those few seconds and remain alive forever. The Doctor must stop him -- but even now, Edith and Charley are in the realm of the potentially dead, playing out the moments which will ensure that the paradox occurs. The Doctor can only reach him if he becomes the next murder victim, and he thus orders Shaughnessy to kill him. As a loyal butler, Shaughnessy can’t disobey a direct order from a gentleman, and despite Edward Grove’s protests, Shaughnessy begins to throttle the Doctor to death.

In the darkness, Edith hands her knife to Charley, telling her to stop pretending to be alive. At the last moment, the Doctor arrives and urges her to stop and think. Given the choice, the Doctor chose to rescue Charley; he chose life over death, regardless of the consequences, and she must do the same. She helped the Doctor to break the curse on Count Orsino and save Earth from the Cyberlords; he showed her wondrous alien worlds and gave her the chance to make a difference in the Universe. She was dead, but no longer; she drops the knife, choosing to live. Edith, however, is still just a servant, trapped in a pointless existence, living only to serve her masters -- nothing and nobody. She will never see the wonders Charley has seen. Urged on by Edward Grove, it appears that she’s about to slit her wrists anyway -- but the Doctor tells her that if she kills herself, she’ll be trapped in this loop forever. Charley promises to remember Edith on all of the alien worlds she visits, and Edith thus chooses to live, no matter how bad things seem. She is not nothing. The paradox is resolved, and Edward Grove dies, pleading for the life which it never had in the first place.