“Six months later”
A man is begging someone to stop a project, that someone is a familiar face … ‘Margaret Blaine’. Bad news for him as he admits that he hasn’t shared his concerns with anyone else.
Mickey arrives by train in Cardiff. He knocks on the door of the TARDIS and Jack answers. Not the most promising start and Mickey is unimpressed, “cheesy” he calls Jack, after calling the Doctor “Big Ears”.
Margret is going to demolish Cardiff castle and build a nuclear power station in the middle of the city and apparently everyone thinks this is a sane plan?!
A local reporter has been researching the string of deaths associated with the project and starts questioning Margaret. Just as things are looking very bad for the reporter she explains that she is pregnant, and unexpectedly Margret feels sorry for her. She’s lonely and lets the woman leave unharmed.
The Doctor and friends are having lunch and listening to one of Jack’s tall tales when the Doctor sees Margret’s photo on the front of a news paper.
The four go to confront her. The Doctor takes the frontal approach and gets her secretary to announce him. The man returns with some lame excuse, the Doctor smiles “She’s climbing out the window isn’t she?”
She’s quickly cornered, having failed to teleport away thanks to the Doctor’s sonic screwdriver. Back in the office the Doctor examines the power station model and declares it to be a plan to open the inter-dimentional rift that lies beneath the city. The Doctor is briefly distracted by the name of the project, it’s Welsh for Bad Wolf. Rose is worried too, but then the Doctor dismisses it as a coincidence and gets back to the matter in hand. The reason Margret wants to open the rift is to power a tribophysical waveform macro-kinetic extrapolator which she would then use to escape Earth. Jack eagerly takes possession of it.
Margret is taken to the TARDIS and it’s agreed by everyone else that she should be returned to Raxacoricofallapatorious. She’s not happy as she faces a death sentence there, but nobody is very sympathetic. She starts playing mind games, questioning if they can knowingly take her to her death with a clean conscience.
Mickey and Rose go off for pizza while Jack and the Doctor set about trying to use the extrapolator to power the TARDIS.
Margret says she wants a last meal and with some insurance provided by Jack the Doctor agrees. Her attempts to kill him during the meal are funny and obviously unsuccessful.
While this is going on Rose is telling Mickey about her adventures and suddenly he bursts out and announces that he’s seeing someone else. At first it seems that she’s fine with it, but then she questions his choice of new girlfriend and he bitterly says that at least he knows where she is.
As Margret continues to beg for her life, trying to convince the Doctor that she can change, the ground starts to rumble. An earthquake? No, the rift is opening above the TARDIS.
The Doctor and Margret make it inside to find Jack trying to disconnect the extrapolator. Rose arrives and is immediately grabbed and held hostage by Margret. She planned the whole thing, if she was captured before the power station plan was completed the extrapolator was programmed to draw energy from any advances technology it was connected to and use the power to open the rift.
As she gloats a panel opens in the TARDIS console and Margret stares into the time vortex. She looks up smiling at the Doctor says “thank you” and then her skin suit colapses empty.
The Doctor and Jack get the extrapolator turned off and the rift closes. Searching the skin suit they find a Slitheen egg. The TARDIS has regressed Margret back to an egg. They can now return her to Raxacoricofallapatorious, leaving her with another family and the chance to have a different life.
Rose runs off to look for Mickey. He sees her but watches from a distance looking sullen, then turns and leaves. Rose returns to the TARDIS saying simply that Mickey’s gone.