The Reception

As promised The Doctor returns Martha Jones home – in fact the TARDIS materialises in her living room 12 hours after she left with The Doctor.

While they are saying their good-byes Martha’s phone rings and when the answer phone picks up the call it turns out to be her mother announcing that her sister Tish is on the news. Martha turns the television on and, alongside Tish, an elderly man, Professor Richard Lazarus, announces that tonight he "will change what it means to be human".

This statement interests The Doctor and so he and Martha become involved in another adventure together when they both attend Professor Lazarus' reception that has been arranged that evening. There The Doctor gets to meet Martha's mother Francine, and her brother Leo and Tish. Francine, concerned for her daughter, is immediately suspicious of The Doctor but before she can talk to him Professor Lazarus arrives and announces they are about to witness a "miracle" – before entering a capsule that is in fact a Genetic Manipulation Device.

Meeting the Jones Family

But the system soon overloads and The Doctor has to quickly disable the machine to avert disaster. As the machine comes to a stop, Lazarus exits from the capsule, as a much younger man. It seems that his experiment has been a success. But has it?

The Doctor is highly concerned of the unknown side effects of this manipulation of Lazarus’ DNA to make him younger. The Doctor is certain there are dangers the professor has overlooked and of course he is proved correct.

Professor Lazarus - Before

After obtaining a sample of Lazarus' new DNA and, with Martha's help, The Doctor discovers that his DNA is highly unstable. Lazarus is changing and when his partner, Lady Thaw, threatens to have their funding removed, if he does not agree to allow her to undergo the process so they can be young together, he mutates into a large, scorpion-like monster and kills her by draining her life energy, leaving her as a zombie-like corpse, before returning to his human form.

When The Doctor and Martha find Lady Thaw's body The Doctor deduces that Lazarus must need to drain life energy to keep his DNA stable. The Doctor realises that Lazarus has accidentally-unlocked an evolutionary throwback, that has been locked away in dormant human genes, and that if he is not stopped they could all pay the price of his so-called scientific progress. The Doctor realises that they are all in great danger and they have to get all those in the reception to safety – including Martha’s family…

The Doctor lures Lazarus, who has transformed again, away as Martha and Tish use his sonic screwdriver to override the building's security lockdown so saving the remaining guests. Martha then rejoins The Doctor and the two are forced to take shelter in Lazarus' device, The Doctor believing he will not harm his own invention. Unfortunately, Lazarus activates the device, but The Doctor is able to reverse the polarity, causing the field to affect only Lazarus outside of the capsule. When they emerge from the machine they are relieved to find Lazarus in his human form and apparently dead.

Professor Lazarus - After

As the police and medics arrive to take care of the wounded, Lazarus' body is taken away by an ambulance. However, when The Doctor hears a nearby crash, he, Martha, and Tish race to discover the ambulance has crashed, its drivers drained of life. They find that Lazarus is alive again and taking shelter in a nearby Cathedral.

The Doctor tries to reason with Lazarus but is unable to stop him transforming again. Martha and Tish, under The Doctor's orders, lure the creature to the top of the Cathedral's bell tower, while The Doctor manipulates the church's pipe organ to produce the maximum volume it can. The vibrations caused by the organ interfere with Lazarus' manipulated DNA, and he falls to his death to the floor below, transforming one last time to his human form.