The TARDIS arrives in late 80's Perivale,at Ace's suggestion only to find that many of the residence,including many of Ace's mates,have mysteriously disappeared as she (apparently) had. Only they are not off with space/time travelling time lords. Each of these disappearances is accompanied by the presence of a black cat. While Ace searches for her friends and the doctor for clues to this mystery,they both end up on a dying alien planet the doctor recognizes as the planet of the cheetah people. Normally a playful race,these cheetah people are now pawns to a major problem along with the Doctors old nemesis The Master. He along with the cheetah's are now linked to the dying planet,which amplifies violent thoughts. While the Master attempts to keep control,Ace and her friend Midge soon fall under the planet's spell. The doctor uses this to every ones advantage to get Ace and her friends home. However the Master has merged with the mind of the living planet to become an even deadlier presence. And the doctor is forced to feign his own death,and Ace has to face the very real death of her transformed sister before she departs back into the cosmos with the doctor she trusts most.
With most of the doctors famous adversaries covered in the programs silver anniversary season,one had been left out-perhaps deliberately. And that was the master. Usually every bit the doctors doppelganger in the sense that he always used his great self control to manipulate and control others,in this case the Master is undergoing an identity crisis.His deviously intelligent mind if being fueled by the primal hostility of a living planet. And along with the mistakes made by an arrogantly aggressive human self defense teacher in this serial,it brings out that it typifies the general message of Doctor Who itself. And that's the message of brain over brawn being the more preferred method of what the Master keeps referring to as "survival of the fittest". Also Ace's story comes full circle. She started as an insecure young lady in need of guidance. And by the time,between being the catalyst for her own existence and knowledge of her being used as a "wolf of Fenric",had grown much more confident and strong of will in the process. It would be seven more years until Sylvester McCoy's seventh doctor regenerated into Paul McGann's eighth. This may have theoretically made him the longest character to play the doctor next to Tom Baker,although present for much of that time only in novels and radio plays of Doctor Who. But even though it's original run was over,this would luckily not be the last time we'd be hearing from this maverick time lord.