Morestrans were humans who had colonised the planet Morestra, and had then built a space-faring empire which spanned eighty million light-years and contained fourteen hundred twenty-seven inhabited star systems by the 372nd century.
Morestrans used probe ships — a far ranging spacecraft — as one means of transport. These ships were equipped with force fields, cyclostimulators and atomic accelerators. They also possessed teleportation technology that allowed objects — such as the Doctor's TARDIS — to be fitted with a device that would transfer the desired item to their ship.
When Morestra's sun began to die, scientists pursued alternate sources of power. This pursuit led Professor Sorenson to take an eight-man expedition to Zeta Minor, the planet farthest out in the known universe. He soon discovered that anti-matter minerals provided anti-quark energy which Sorenson believed could be harnessed to provide a huge amount of power.
However, the expedition came under attack from an anti-matter creature. The Morestrans sent a probe ship under the command of Controller Salamar to discover what had become of Sorenson's team as no word had come since their arrival on Zeta Minor.
Having landed on the planet, the Morestrans discovered the Fourth Doctor and Sarah Jane Smith and believed them to be responsible for the deaths of the crew of the previous expedition. The anti-matter minerals were taken aboard the probe ship. When they attempted to take off, the cyclostimulators failed and the creature attacked, unwilling to let them leave with the minerals on board. The Doctor gained the confidence of Salamar and his right-hand man, Vishinsky, by instructing them to link the atomic accelerator to the force field, allowing them to repel the attack. The Time Lord negotiated with the creature, promising to return all the anti-matter.
Salamar had the minerals jettisoned, but Sorenson secreted a canister. He became infected by the anti-matter and degenerated into what the Doctor labelled "anti-man". Bestial in appearance and savage in act, Sorenson killed three of the crew: Morelli, De Haan and Reig. The ship managed to travel some way off the ground, but then the pull of gravity began to increase, pulling the ship back towards the planet due to the minerals continued presence on board. The ship was set to collide with the surface.
Due to Salamar's mishandling of the affair, and his attempts to pin the blame on the Doctor and Sarah, Vishinsky assumed control. The deposed Controller turned on his comrades, killing one and forcing them to open the doors of the ship, allowing him to pursue Sorenson. The professor killed Salamar, who dropped an neutron accelerator he had intended to use, creating pure anti-matter duplicates of Sorenson. These created havoc on the ship, attacking the crew.
The Doctor gathered the remaining anti-matter and, taking Sorenson too, returned in his TARDIS to the planet's surface. He returned the minerals and sent the infected scientist to the anti-matter dimension. The promise having been kept, the duplicates vanished and Sorenson was returned to his former self.
Vishinsky hoped the ship would be able to receive an emergency refuelling after they had travelled closer to home. Professor Sorenson, having lost most of his memory, was convinced by the Doctor that he had been looking into harnessing the kinetic force of planetary motion as a new alternate power source. (TV: Planet of Evil)