The Seventh Doctor and Ace learn of a property in Croydon where a tree just vanished into thin air and decide to investigate. They soon discover Joe Dakin, an unwilling time traveller who has been forced to transcend the dimensions by some exterior force. The one responsible soon reveals itself, a biomechanical Virgoan space probe in the form of a pigeon that has been sent to repair temporal glitches and anomalies yet was invaded by a Krynoid influence while on Melandra IV, the battle for control being amplified across any surrounding machinery and vegetation. The probe transports Ace and Joe eighty years into the future where they discover the Master has been sucking the elderly dry, using their life-force to sustain himself and stave off the curse of the Cheetah World. His stock never fades as he fools people into handing over their loved ones with the promise that they will be rejuvenated. He merely uses the Virgoan probe to send hypnotised innocents back in time to collect the elderly when they were infants, thus keeping the illusion alive. The plan falls through when the battle is amplified across the retirement home causing all the machinery and vegetation to tear each other apart and leaving the entire facility nothing but rubble. The Doctor is left to clean up the mess as the Master escapes yet again.
The Master is still infected with the cheetah virus, although another account claims after leaving the planet he was immediately cured and given a new regeneration cycle by the Tzun. (PROSE: First Frontier)
The Doctor and Ace will encounter the Master again, still infected with the cheetah virus. (PROSE: Prime Time
According to one account, the Master had the appearance of Roger Delgado while on Gallifrey. According to another, he had Anthony Ainley's likeness. According to another one, the one with James Dreyfus's appearance was the incarnation who ran away from Gallifrey.
While fighting to extend his life at the end of his regeneration cycle, many bodies were possessed by the Beevers incarnation but all kept somehow reverting to his real being until he finally regenerated into the MacQueen one. Hence, these sections cannot be strictly chronological