England, the near future. A strange anti-matter creature arrives on Earth and attacks UNIT HQ. It seems to be specifically seeking the Doctor out - but why? With the Time Lords themselves unable to help, it seems the only person who can help the Doctor is himself - or selves...

The third Doctor and Jo find themselves on an artificial world inside the black hole while the second Doctor tries to find a way to control the organism.

The Time Lord Omega reveals himself to the third Doctor along with plans for vengeance against his own kind.

Omega reveals the purpose behind bringing the Doctor to his antimatter world, but the Doctor(s) discover a startling fact about Omega that he didn't know himself and eventually strike a bargain.