In an office overlooking the city, Professor Richard Lazarus (the gentlemen from the television report) and Lady Thaw look out into the night. Lazarus assures his austere counterpart that the upcoming experiment will work and give the audience as well as Mr Saxon what they are waiting for.
Tish Jones enters with a guest list for the evening and waylays some amorous advances from her learned employer; whilst outside the Doctor and Martha, both in evening dress, make their way toward the Lazarus Laboratories building. Inside stands a magnificent machine, a chamber surrounded by shining columns.
Tish arrives and greets her sister, before introducing the Doctor. Soon Martha’s mother Francine arrives with her son (Martha’s brother) Leo, and Martha greats them both warmly. Awkwardly she introduces the Doctor, who only succeeds in arousing suspicion about his relationship with Martha from her concerned mother.
Lazarus then takes to the stage, claiming his experiment will signify a great scientific advance. He steps inside the central chamber of the machine, which is then activated. The smaller columns begin to rotate as the machine is bathed in blue light. Suddenly alarms ring out and the Doctor is forced to turn the device off before it overloads. Lady Thaw protests but he succeeds in stopping the machine, and Martha opens the door.
From within steps a somewhat startled young man, wearing the same clothes as the elderly Professor Lazarus. He staggers forward and announces:
“Ladies and gentlemen. I am Richard Lazarus. I am 76 years old; and I am reborn”
The Doctor looks on with an icy look as Lady Thaw congratulates her friend, who suddenly succumbs to ravenous hunger. The Doctor steps in and identifies it as an energy deficit and then begins to talk about the experiment, noting that Lazarus could not have allowed for all possible variables in the outcome.
Lady Thaw claims the Doctor is not in a position to comment and Lazarus insists that he is fine; he has created a way for humanity to improve. The Doctor dismisses this but Lazarus and Thaw leave, the former kissing Martha’s hand before moving off. The Time Lord claims that they should run some tests to check the machine and Martha points out that she now has a DNA sample on the back of her hand.
Back in their office Lazarus and Lady Thaw discuss growing up in the Second World War, Lazarus having spent time hiding in Southwark Cathedral during the Blitz. The pair kisses but Lazarus draws back, apparently disturbed by the visual age gap between them.
In another laboratory the Doctor and Martha examine Lazarus’s DNA, shocked to find it constantly changing, something laying dormant in his genetics has been unleashed in the process of renewal, and is now trying to change him. Realising the risk they run upstairs to find him.
Lady Thaw is furious to think Lazarus will cut her out of the profit of the experiment and claims that if she too is rejuvenated they can be rich and young together. Lazarus mocks the idea but suddenly begins to contort unnaturally. He falls to the floor and writhes in agony, apparently changing. Lady Thaw looks on as Lazarus gazes upon her with inhuman eyes.
In the reception area Francine is curious to find out more about the Doctor, finding him somewhat peculiar. Lazarus soon arrives, now wearing a different shirt. He approaches Tish and whisks her away.
The Doctor and Martha arrive in Lazarus’ office, finding the husk of Lady Thaw’s body awaiting them, now devoid of all life energy. They realise that Lazarus needs such energy to cater for the dormant genes, and so he will kill again. They hurry downstairs, only for Tish and Lazarus to arrive in the room moments after they leave.
They ascend to the roof to admire the view whilst downstairs the Doctor and Martha discover where Lazarus has gone. They hurry away whilst a mysterious man, who enquires as to the Doctor’s presence, approaches Francine.
On the roof Lazarus and Tish admire the view of Southwark Cathedral. Tish leans forward and gently strokes the man’s skin, asking if the outcome of the experiment is as he expected. He replies in verse:
“Between the idea
And the reality
Between the motion
And the act…”
“…Falls the shadow.”
The Doctor finishes his recital and warns that the experiment is a curse. Suddenly he falls to the floor again and reappears a hideous monster, some way between a spider and a scorpion. The Doctor, Martha and Tish run inside as the security alarm is sounded and the building is locked down.
They flee downstairs and Martha uses the Sonic Screwdriver to try and open one of the exits. Suddenly Lazarus, still in monster form, arrives and chaos breaks out, as the monster feeds on another victim. The Doctor mocks him then runs, the creature chasing him along a corridor. They arrive in a boiler room as Martha manages to open up the front doors, allowing the guests to flee outside. The Doctor flees from the boiler room and the chase continues, whilst Martha vows to return to find her friend, against her mother’s wishes.
Arriving in another laboratory the Doctor begins to tamper with the wiring of the lighting and starts turning on all of the methane gas taps. Lazarus enters but the Doctor manages to escape, flicking the light switch and creating a massive explosion. He continues to run and finds Martha awaiting him, but Lazarus is not dead yet.
Outside Francine worries about the Doctor and Martha, the mysterious man returning again to warn her that the Doctor is a dangerous man, whispering something in her ear. Back inside the Doctor and Martha take refuge in Lazarus’s machine; hoping the creature will not attack his own masterpiece.
However with no further plan the Doctor is left to improvise and begins zapping the chamber with the Sonic Screwdriver whilst Lazarus stalks around outside, eventually switching the machine on. As light floods into the chamber the Doctor manages to reverse the polarity of the machine and it zaps Lazarus, who returns to human form. The two time travellers step outside to find Lazarus slumped on the floor.
“This is the way the world ends
Not with a bang but a whimper”
Soon Lazarus’ body is being taken away in an ambulance and the Doctor and Martha are confronted by Francine, who slaps the Time Lord and warns him to stay away from her daughter. She tells Martha that he is dangerous and begs her to leave him, but she cannot, and follows him as he dashes off following the sound of a distant crash, Tish also in tow.
They arrive to find the ambulance crashed and Lazarus escaped, tracing him to Southwark Cathedral. Inside all is dark, and as they ascend the aisle they find Lazarus, draped in an alter cloth, cowering in fear. He remembers being in the Cathedral when he was a child. He boasts again about changing the course of history but the Doctor claims that facing death is all part of being human.
Lazarus again fights the DNA override, and the Doctor whispers to Martha that he has an idea; he needs to get Lazarus into the bell tower. He turns to Lazarus and warns him that the only certainty of a long life is that you will end up alone. Lazarus prepares to feed and Martha uses herself as bait. She and Tish ascend the staircase and as Lazarus finally transforms once more, he follows.
The Doctor arrives at the Cathedral’s giant pipe organ, and as Martha, Tish and Lazarus ascend to the bell tower he begins to play. The mutated creature almost succeeds in dropping Martha through the tower and onto the stone floor far below, but when the Doctor manages to maximise the hypersonic sound waves of the organ the creature is overcome, plummeting to down into the abyss.
Safe once more, Martha and Tish join the Doctor down below, where once again Lazarus’s naked human body lies motionless. The Doctor leans forward to close the man’s eyes, as he reverts back to his original elderly form.
Some time later the Doctor and Martha are back outside the TARDIS. She warns him to take more care wherever he goes next and he offers one more trip with him. She declines, no longer content with being just a passenger. He agrees that she is more than that and together they depart one more.
As the ship fades from view the telephone rings. Switching to the answer phone Francine’s voice is heard
“Martha it’s your mother. Please phone me back I’m begging you. I know who this Doctor really is; I know he’s dangerous. You’re gonna get yourself killed. Please trust me. This information comes from Harold Saxon himself, you’re not safe.”