Will Barton

Vital organs are missing from murder victims; Brogan may be next.

Prisoners take over maximum security asteroid A-5, trapping Castle and Haldane.

The Doctor and a number of people from Perivale follow Ace to the Cheetah-People's world, where the Master lies in wait. He cannot leave without the Doctor's assistance.

The Doctor takes Ace on a sentimental trip to her old neighbourhood, only to find that something nasty is stalking the streets of Perivale.

The Doctor and Ace move towards their final confrontation with the animal in us all. The Doctor must also face the Master, who is becoming that animal. Is this their last ever duel?