RESPONDING TO AN AUTOMATIC DISTRESS SIGNAL, the Doctor and Sarah Jane Smith arrive on Zeta Minor, a jungle world at the edge of the known universe, in the year 37,166. They find the deserted base camp of a Morestran expedition and that seven men have died there in mysterious circumstances. The only survivor is Professor Sorenson, who claims to have discovered a means of exploiting antiquark energy to refuel his home planet’s dying sun.
The arrival of the TARDIS coincides with that of a Morestran probe crewed by a military unit on a mission to recover the expeditionary team. Discovering the Doctor with the mummified corpse of one of the scientists, the ship’s hot-headed controller, Salamar, jumps to the conclusion that the Doctor and Sarah are responsible for the deaths and orders their execution. Fortunately, his experienced first officer, Vishinsky, is prepared to listen to the Doctor’s explanation: that the planet lies on the threshold of a parallel antimatter universe and Sorenson’s intention to extract antiquark minerals has upset the balance of nature.