The Doctor takes Ace back home to Perivale so she can catch up with her old friends. But Perivale has changed, the old gang has split up, and some of them have vanished without trace along with many other residents. The pair find some signs of life in a self defense class being taught by Sgt. Patterson. There's also something a bit odd about the black cats around town.

The Doctor decides to try and lure one of those cats closer by putting down some cat food. While he is busy, Ace decides to do a little further exploration on her own. Oddly enough, she catches the attention of a black cat. A Cheetah man riding a horse suddenly appears behind her and chases her around a playground. With no where left to run, Ace mysteriously disappears in a flash of light and reappears on a strange planet. This is apparently where Perivale's residents have been taken, as she finds the corpse of a recent victim lying nearby on the ground.

After evading a few more Cheetah people, Ace comes across a camp and finds a group of her friends. From her friend Midge she learns that the Cheetah people have been transporting earthlings to this planet to hunt and kill. The small group is demoralized and just waiting for their turn to be hunted and caught.

Meanwhile, the Doctor has managed to get close to one of the black cats, but his plans of capturing one are interrupted by Sgt. Patterson, and he finds himself instead being transported along with the Sergeant to the Cheetah people planet. The pair suddenly find themselves in the middle of a camp of Cheetah people who force them toward the entrance to a tent. By this time, the Doctor isn't really that surprised to discover The Master within the tent.

For some reason, The Master was also transported to this planet and his now stuck. He has used his mental abilities to urge the Cheetah people to also bring the Doctor to their planet. His thinking is that the Doctor will somehow be able to find a way off the planet. In his time stuck there, The Master has been developing some decidedly feline characteristics. Seems being on the planet, and using his powers to control the Cheetah people has come at a cost.

The Doctor manages to get himself and Patterson away from this encampment, and it isn't long before he finds Ace and her small group of Perivalians. The Doctor and the group don't have much time. The planet is in the process of disintegrating and in order to get to a place of relative safety, they must travel through a group of Cheetah people. The Doctor advises them to remain calm and not run, but the others panic and soon are separated and hunted by Cheetah people. Midge manages to turn the tables and kill one of the Cheetahs, but it has an adverse affect on him.

When the group is able to rejoin, it doesn't take long for the others to see that Midge has begun changing into a Cheetah man. The Doctor realizes that Midge may be their ticket home, as the cheetah people are the only ones capable of transport on or off the planet. Unfortunately, The Master over hears this, and soon has captured Midge and forced him to return to earth, leaving the Doctor and friends behind. Their only hope now is to wait for one of the others to change as Midge did. Turns out that person is Ace.

Before Ace can completely transform, the Doctor convinces her to take them all home. Back on earth things aren't over, however. The Master has coerced Midge and Sgt Patterson's self defense class into attacking the Doctor. The Doctor is momentarily shaken by an explosion and it looks like Ace is all alone to face the angry students. She is suddenly rescued by the appearance of a Cheetah woman who has taken a shine to Ace. Unfortunately, The Master stabs the Cheetah woman, and she returns to her human form as she dies.

In a last ditch effort at revenge, a very feline Master transports a recovered Doctor back to the Cheetah planet. As the planet falls apart around them, the pair struggle together. The Doctor appears to also have begun transforming into a beast, and he is tempted to give in and destroy The Master. He catches himself and is able to reassert control, but not before he uses his Cheetah ability to transport back to earth. The Master is left behind to his fate.

The Doctor and Ace regroup and return to the TARDIS and begin their next journey.