The TARDIS materialises in Ferrara on 11 July 1982. Italy has just beaten West Germany 3-1 in the World Cup final, but the Doctor and Charley aren’t here for the celebrations, wild though they may be. The TARDIS has detected an interspatial disturbance in the forest outside town, and when the Doctor traces it to its source, he finds two Threllip soldiers -- Captain Vengorr and his subordinate, Thon -- setting up an interdimensional portal for the Threllip army to pass through and invade Earth. The Threllip, a dull but aggressive species, are so technologically advanced that they’ve even had dealings with the Time Lords. As the Doctor and Charley listen from hiding, the pompous Vengorr, bored by the simple task he’s been assigned, pontificates on the nature of destiny and tells the long-suffering Thon that he’s always believed that he is destined for great things. This gives the Doctor an idea...

The Doctor and Charley thus retreat to the TARDIS and make a short hop to the forest clearing, materialising before the startled Vengorr and Thon. With much grandiosity, the Doctor emerges and introduces the Threllip to his superior, the Time Lady Charleyostiantayshius, claiming that they are here to observe Vengorr’s actions. Despite Thon’s suspicions, Vengorr’s interest is successfully piqued, and he demands, at gunpoint, to know why the Time Lords have chosen to observe him. Charley chastises the Doctor for overstepping his bounds and allowing “Vengorr the First” to know too much, and reveals to the stunned Vengorr that he is destined to lead the invasion of Earth after the commander of the Threllip forces is struck down by a fatal illness -- and that his brilliant leadership will mark him out as a hero of the Threllip Empire.

Vengorr avidly takes this all in, and demands to know the details of his ascension to power. The Doctor thus volunteers to take him into the local town to meet the natives who will become the first slaves of his new regime. Vengorr sets off, leaving Thon to complete his work on the portal. As Thon works, he hesitantly asks Charley what his role in history will be, and, after some thought, Charley announces that he isn’t so much as mentioned in any of the 56 volumes of Vengorr’s memoirs. Thon, who has served as Vengorr’s assistant for over 32 years, listens with barely controlled rage as Charley “happens to recall” a brief mention of a figure named Thon -- Vengorr’s pet wart-snoggler, a rat-like animal which became his platoon mascot.

The Doctor leads Vengorr into Ferrara, where the Threllip captain is shocked by the bizarre gyrations and screams of the local populace. The Doctor sadly reveals that this entire planet has fallen victim to a plague known as World Cup Fever, the same plague which will strike down the commander of the Threllip invasion force. When a cheerfully drunk villager offers Vengorr a drink, the horrified Threllip flings him through the window of a nearby tavern. Fortunately, the villager is only stunned, and after ensuring that he’ll be all right, the Doctor warns Vengorr that World Cup Fever is spread by physical contact. Fortunately, he claims, the tavern is a clinic containing bottles of vaccine. The Doctor urges Vengorr to drink as much of the “vaccine” as quickly as he can before he begins to exhibit the symptoms of World Cup Fever -- loss of co-ordination, slurred speech, and loud belching. However, the more “vaccine” Vengorr drinks, the worse the “symptoms” get...