Having been unable to prevent the theft of the TARDIS from Gatwick Airport the Doctor and Jamie quiz the hangar foreman, Bob Hall (Alec Ross). The Doctor grows suspicious of him and decides to follow him when he leaves. Kennedy (Griffith Davies), an accomplice of Hall's who has been keeping watch, reports this to his boss Edward Waterfield (John Bailey), a Victorian-garbed antiques dealer. Waterfield's assistant Keith Perry (Geoffrey Coleville) comments on the collectability of the police box that now sits in the workshop. Waterfield tells him that they pander to the desires of their clients . 

The Doctor and Jamie track Hall to a warehouse, where he has been left unconscious after a struggle with Kennedy. He eventually recovers and flees, leaving behind a box of matches from a coffee bar called the Tricolour. The Doctor tells Jamie they must find this place in the hope that Hall will turn up there. 

Kennedy tells Waterfield that he planted the matches as instructed and that the Doctor is following the trail of clues left for him. He hands over photos of the Doctor and Jamie which Waterfield later gives to Perry, telling him to meet these new 'clients' in the Tricolour and arrange for them to come to the shop at ten o' clock that evening. When Perry has left, Waterfield opens a door to a hidden room that contains an advanced machine. 

In the coffee bar the Doctor tells Jamie that he is sure they are being led into a trap. Perry relays Waterfield's message and the Doctor promises to visit the shop at ten. 

While Waterfield prepares for the Doctor's arrival Kennedy snoops around and discovers the hidden room. The machine within activates, and a Dalek materialises and blasts him down. 

The Doctor and Jamie arrive early in order to investigate. They notice that all the supposed antiques look brand new, although the Doctor is sure that they are genuine. Jamie wonders if Waterfield has created a time machine. 

Waterfield discovers Kennedy's body and is aghast that the Dalek has killed. The creature tells him that only Dalek life is important and that he must fulfil his mission. It then fades from sight. 

Jamie and the Doctor encounter Perry, who agrees to answer their questions about Hall and tells them where the TARDIS is being held. They then discover Kennedy's body and Perry goes to fetch the police. The Doctor and Jamie gain entry to the hidden room but are rendered unconscious by gas from a booby trapped box. 

The Doctor wakes to find that he and Jamie are now in the drawing room of a large country house. He learns from a maid, Molly Dawson (Jo Rowbottom), that it is the home of Theodore Maxtible (Marius Goring) some miles outside Canterbury. Maxtible and Waterfield enter and reveal that the date is 2 June 1866. The Doctor accuses the men of the theft of the TARDIS and the murder of Kennedy. Waterfield protests that he was not responsible for the man's death and Maxtible remarks that they are all victims of a higher power which holds Waterfield's daughter Victoria hostage. Waterfield begs the Doctor to co-operate as the girl's life depends upon it. 

Victoria (Deborah Watling) is being kept prisoner by the Daleks in another room of the house. 

Maxtible takes the Doctor to his laboratory and tells him of his experiments into time travel using mirrors, magnetism and static electricity. Waterfield explains that during their last experiment, involving a room-sized cabinet, strange creatures burst out and took over the house, seizing his daughter as a hostage. The monsters forced him to travel into the future and set a trap for the Doctor. The Doctor anxiously asks the creatures' identity and his question is answered by the sound of a familiar grating voice. A Dalek appears and tells him that unless he conducts a series of tests on Jamie the TARDIS will be destroyed. It then glides out again. Maxtible speculates that the creatures' aim is to analyse a human being to discover the 'human factor' that has made them so successful in battling the Daleks. The Doctor is concerned this will make them even more dangerous than before. 

Jamie wakes and meets first Molly and then Maxtible's daughter Ruth (Brigit Forsyth). Left alone in the room he starts to investigate but is knocked unconscious by a thug called Toby (Windsor Davies). Molly returns and is likewise accosted by Toby, who puts her senseless body into a chair and carries Jamie away. On learning what has happened the Doctor tells Waterfield that unless they can find Jamie the Daleks will happily kill everyone in sight. 

Toby has shut Jamie in a nearby stable. He claims that he was paid to kidnap him by Ruth's fiancee, Arthur Terrall (Gary Watson). Terrall arrives and first admits this and then denies it. Toby runs off and Jamie is left with the seemingly unhinged Terrall. The Doctor then enters, having thought to check the stable after finding a piece of straw in the drawing room. Terrall makes his excuses and leaves. 

The Daleks move Victoria to another part of the house. They and Maxtible are arranging for a mute Turkish wrestler called Kemel (Sonny Caldinez) to prevent Jamie from rescuing the girl. 

The Daleks tell the Doctor that they wish to insert the human factor into three of their number brought from their home planet Skaro in a dormant state. The Doctor reluctantly agrees to help. 

Ruth tries to introduce Terrall to Jamie but discovers they have already met. An argument between the two men is halted only when Terrall suffers some sort of seizure. 

Jamie overhears the Doctor plotting with Waterfield and angrily confronts him. The Doctor warns him not to try to rescue Victoria. When he has gone the Doctor admits that he engineered the whole argument, knowing that it would goad Jamie into action. 

Toby meets Terrall and tells him that he wants the money he was promised. Terrall again suffers an attack and collapses. Toby decides to loot the house. 

That night, Molly gives Jamie a plan of the house to aid his attempted rescue of Victoria. The Doctor and the Daleks are secretly watching the young Scot and recording all his reactions. Toby is also present but falls victim to one of the deadly traps set for Jamie. Jamie proceeds carefully but eventually encounters Kemel, who attacks him. Jamie emerges from the struggle victorious, saving Kemel's life when he stumbles into another of the traps. 

The Doctor notes Jamie's courage in fighting Kemel and mercy in rescuing him. The Daleks will need both qualities if they want the human factor. Waterfield and Maxtible have meanwhile discovered Toby's body. The Daleks order them to hide it from the Doctor. A distraught Waterfield states that once his daughter is free he intends to confess to the authorities. Alarmed, Maxtible tells him that neither of them are guilty. Terrall attempts to kill Waterfield but is stopped by Maxtible. 

The Doctor continues to monitor Jamie's reactions as he and Kemel - now friends - make their way through the house, narrowly avoiding yet more lethal devices. The two men eventually reach Victoria's room and plan to draw off the Daleks guarding the door. The Doctor points out that in avoiding a suicidal attack Jamie is showing self-preservation - another important element of the human factor. 

Maxtible gains an assurance from the Daleks that they will honour their promise to give him the secret of turning base metal into gold 

Jamie and Kemel manage to destroy the two Daleks guarding Victoria's room. They join her inside and barricade the door with furniture. 

The Doctor questions Terrall abut the fact that nobody in the house has ever seen him eat or drink. When Terrall threatens him with a sword, the Doctor notices that the blade has become magnetic as if the man is charged with electricity. Waterfield calls the Doctor away and Terrall again suffers an attack, hearing a voice telling him to obey. 

Maxtible hypnotises Molly and commands her to forget the strange events she has witnessed. He tells Terrall that he used the same technique on Victoria, but that her father's usefulness is now at an end. Terrall asks for relief from the attacks he is suffering and Maxtible promises to help once Victoria has been fetched. Again Terrall hears the voice telling him to obey. 

The Doctor tells Waterfield that the human factor is now stored in the positronic brains that will be implanted into the three dormant Daleks. Waterfield begs him not to proceed, fearing that it will mean the creation of creatures that will overrun the universe. The Doctor replies that it is too late to stop, although events may not take the path that the Daleks are expecting. 

Terrall sneaks into Victoria's room via a secret passage and drags her away. Jamie and Kemel follow but are forced to split up when the passage forks. Jamie catches up with Terrall, who no longer has Victoria with him, and they duel with swords. The Doctor and Ruth arrive just as Terrall collapses. The Doctor tells Ruth that to save her fiancé's life she must take him far away. 

The Daleks have Kemel take Victoria into the time cabinet. Jamie is meanwhile growing increasingly distrustful of the Doctor. The three Daleks with the human factor enter the laboratory but seem more interested in playing games than in conquest. The Doctor explains that they are the equivalent of children but that they will grow up fast. He nicknames them Alpha, Beta and Omega. 

The Daleks tell the Doctor that they have all been ordered back to Skaro. Waterfield learns that Maxtible was responsible for his daughter's kidnapping and attacks him. Maxtible knocks him out but then discovers the Daleks have set a bomb that will destroy the house. He escapes into the time cabinet. A recovering Waterfield warns the Doctor and Jamie about the bomb. They all get into the cabinet and escape just before it explodes. 

On Skaro, a Dalek escorts Maxtible into a room where Victoria and Kemel are being held. A siren sounds, indicating that other humans have entered the city. The Doctor, Jamie and Waterfield have made their way into the subterranean city through cavernous tunnels. They hear Victoria scream and, in his eagerness to go to her aid, Jamie nearly falls down a sheer drop. At the edge of the city a Dalek identifying itself as Omega meets the group and offers to lead the way. The Doctor spots that it is an impostor and pushes it over the precipice. 

Victoria has been forced to scream by Maxtible, who is still following Daleks commands. She realises that the Daleks are trying to lure the others into a trap. The Doctor, Jamie and Waterfield are captured and taken before the enormous Emperor Dalek. The Doctor asserts that the three Daleks with the human factor will start to question orders and cause a rebellion. The Emperor reveals that the Daleks' true motivation for acquiring the human factor was to help them to isolate the Dalek factor. They now want the Doctor to implant the latter into humans throughout Earth's history using the TARDIS, which they have brought to Skaro. 

The Doctor and his friends are locked up with Maxtible. The Doctor tells Victoria that he will not accede to the Daleks' demands even if it means all their deaths. He questions Maxtible about the device that the Daleks used to control Terrall. The Daleks show Maxtible a machine that can transmute iron into gold. Maxtible moves forward to inspect it, but as he passes through an archway the Dalek factor is inserted into his brain. He is now mentally a Dalek. 

That night Maxtible tries to infect the Doctor with the Dalek factor and appears to succeed. The Doctor goes with him to work on the plan to spread the Dalek factor on Earth. Once on his own, however, he goes back to the others and tells Jamie to lead them through the archway. Still pretending to have been converted, he then tells the Emperor that all Daleks should pass through the archway so that the humanised Daleks will be converted back into true Daleks. The Emperor agrees. 

The Doctor reveals to Jamie and the others that the archway could not affect him as he is not human. He has now swapped the Dalek factor for the human factor so that when the Daleks pass through the archway they will all be converted. He tells his friends to head for the surface, where he will join them. Waterfield decides to go back into the city to find Maxtible. The converted Daleks spread through the city and soon civil war breaks out. The Doctor tells the converted Daleks to seek out the Emperor as he has ordered their destruction, and they join battle with the Emperor's black Daleks. Seeing an enemy Dalek approaching, Waterfield shields the Doctor and receives a fatal wound. Before he dies he asks the Doctor to take care of his daughter. 

As the friends make their way out of the war-ravaged city they encounter Maxtible and a Dalek. Jamie manages to throw the Dalek over the edge of the precipice, but Maxtible sends Kemel to the same fate. Maxtible then returns to the city, but is killed in the explosions ripping through it. The Doctor meets up with Jamie and Victoria and breaks the news of Waterfield's death. He tells Victoria that it was not in vain as he believes that this is the final end of the Daleks. They head for the TARDIS and safety.

_{Synopsis from Doctor Who: The Second Doctor Handbook by David J. Howe, Mark Stammers and Stephen James Walker, reprinted with permission; further reproduction is not permitted. Available from Telos}