Director: Richard Clark (II)
Show Stars: David Tennant (The 10th Doctor (Season 2 - )), Freema Agyeman (Martha Jones (Season 3 - ))
Recurring Role: Adjoa Andoh (Francine Jones)
Guest Stars: Bertie Carvel (Mysterious Man) , Mark Gatiss (Professor Lazarus) , Thelma Barlow (Lady Thaw) , Gugu Mbatha-Raw (Tish Jones) , Reggie Yates (Leo Jones) , Lucy O'Connell (Party Guest)
Production Code: NCFT086K
The TARDIS materializes on Earth in Martha’s era, in her bedroom 12 hours after she left. Martha’s mother calls to say her sister is on TV and Martha tunes in to see her at a press conference held by Professor Richard Lazarus, who says he has developed a way to “change what it means to be human.” The Doctor says goodbye to Martha and she thanks him, then he dematerialize the TARDIS. However, it reappears again seconds later and the Doctor emerges to investigate Professor Lazarus.
Lady Thaw is meeting with the elderly Professor Lazarus, who assures her that their sponsor, Mr. Saxon, will get his money’s worth. Tish Jones arrives and Lazarus tries to flirt with her without much luck. The Doctor and Martha arrive in fancy dress for Lazarus’ party and blend in with the crowd. They find Tish, who says that their mother and Leo will be coming soon. Martha introduces the Doctor, and he tries to find out more about Lazarus.
Francine Jones arrives and Martha tries to introduce the Doctor, but it doesn’t go well since they can’t explain exactly what they’ve been doing. Professor Lazarus arrives and begins his demonstration, stepping into the chamber. However, the equipment goes into overload and the Doctor manages to shut it down. Professor Lazarus emerges from the chamber… now a young man.
Martha is skeptical but the Doctor is impressed despite himself. Lazarus starts eating and the Doctor chats with him about the theory. The Doctor warns that Lazarus couldn’t have taken into account all the variables, but the professor dismisses his concerns and claims everything will be ironed out before they offer it commercially. The Doctor decides to find a laboratory in the building to run some tests and Martha has some DNA from when Lazarus kissed her hand.
Lazarus chats privately with Lady Thaw about the devastation of World War II and the Blitz. They start to kiss but then Lazarus points out how old she is.
The Doctor determines that Lazarus’ DNA is unstable and goes to find him. Meanwhile, Lazarus continues to reject Lady Thaw but he is suddenly seized with cramps and convulsions. He falls to the ground then begins to mutate into a new form, then rears up and attacks her.
At the reception, Francine tries to get more info on the Doctor from Tish, who doesn’t know anything. Francine thinks something is going on, but Lazarus arrives back in human form and asks to meet with Tish. The Doctor and Martha go up to Lazarus’ office and find the withered husk of Lady Thaw’s corpse. The Doctor warns Lazarus might not have acquired enough energy and will need to feed again. They go downstairs just as Lazarus and Tish arrive on the other elevator and go up to the roof for the view. The Doctor talks to Francine but before she can ask him anything, he realizes where Tish is and heads upstairs. As they go, a mysterious man approaches Francine and suggests Martha choose her friends more carefully.
The Doctor and Martha get back to the office and track Lazarus’ DNA signal up to the roof. They confront him there where Lazarus is unrepentant, even thought the Doctor says the time matters less than the person. Lazarus mutates again into a hideous form and attacks them as they head back down to the elevator. The monster’s attack activates the security breech, sealing the building. The Doctor, Martha and Tish run down the stairs as Lazarus comes after them. They get to the reception and Martha tries to get the door open while the Doctor gets the guests out. Lazarus’ arrival convinces them to run and Martha gets the door open so the guests can leave. Lazarus kills one party guest then turns toward Francine and an injured Leo. The Doctor taunts Lazarus into following him while Martha gets her family out.
The Doctor runs into the basement and plays a game of cat-and-mouse with Lazarus. Martha goes back to help the Doctor over her mother’s objections. The Doctor enters a lab and opens the gas valves. He then runs out the door while igniting the gas, causing an enormous fireball to envelop Lazarus. He runs into Martha who returns the sonic screwdriver, but Lazarus has survived and they’re forced to flee.
Outside, Francine is unhappy with Martha’s choice and Tish suggests she might be in love with the Doctor. The mysterious man from earlier suggests there are thing Francine needs to know and whispers in her ear.
The Doctor and Martha take refuge in Lazarus’ regeneration chamber, figuring he won’t destroy his own creation. The Doctor explains that Lazarus’ new monstrous form is some kind of dead-end evolutionary path the machine activated, and begins to rewire the machine. Lazarus activates the machine but the Doctor reverses the polarity and the energy surge throws Lazarus back. They emerge to find Lazarus back in his youthful human form, unconscious.
Lazarus is taken away in an ambulance and a furious Francine confronts the Doctor, slapping him and warning him to stay away from Martha. There’s a crash from the ambulance and the Doctor goes to investigate while Francine tells Martha to leave him. Martha and Tish both go and they all find the EMTs dead. The Doctor tracks Lazarus’ DNA signal to the nearby cathedral and find Lazarus in human form for the moment, having sought sanctuary just as he did during the Blitz. Lazarus tries to justify him and the Doctor warns that immortality isn’t worth it if you’re left alone. Lazarus is willing to pay the price, even as his body is wracked with convulsions.
Martha lures the hungering Lazarus after her and Tish, buying the Doctor time to come up with a plan using the cathedral’s organ. While the mutating Lazarus chases them upward, the Doctor tells them to get him to the top of the belltower. He then plugs his sonic screwdriver into the organ and pulls out all the stops, while Martha and Tish run out of space to run. Lazarus knocks Martha off the catwalk and she holds on while the Doctor hits the Lazarus mutate with enough sound to cause it to fall to its death, where it reverts to Lazarus. Tish pulls Martha to safety while the Doctor witnesses Lazarus revert to his original age.
Back in Martha’s room, the Doctor prepares to leave again and invites Martha for one more trip. She says no, admitting she doesn’t want to be just a passenger and he invites her in and they depart. As they dematerialize, the phone rings and Francine leaves a message warning Martha that she knows who the Doctor really is and that Harold Saxon has warned her how dangerous her traveling companion is.