In this serial, the TARDIS materialises in Earth's future on a space beacon just before it is attacked by pirates, led by Caven (Dudley Foster).
The travellers find themselves trapped in a sealed section of the beacon that is blown apart and flown to where the pirates will plunder it of the precious mineral argonite.
They witness a conflict between the pirates and the Interstellar Space Corps, led by General Hermack (Jack May) and Major Warne (Donald Gee).
The Earth Space Corps cruiser V-41 notices the destruction of the beacon and, with General Hermack and Major Warne in charge, sets out to apprehend the pirates.
Caven and his men kill the security force there, save Lt Sorba, who is taken as a hostage, and the pirates seal the time travellers in part of the Beacon before blowing it to pieces.
Zoe has plotted the trajectory of the segments of the beacon and believes they were headed for Ta as well, and the Doctor and his companions soon find the pirate headquarters.
Meanwhile, Caven forces Dervish to reroute some of the beacon fragments to Lobos, a frontier world where Clancey has his base, so as to throw suspicion on the prospector.
As Hermack’s ship lands, Madeleine looks forward to a reunion with her father, but knows she will also be imprisoned for her part in the conspiracy, while the Doctor and his companions prepare to seek out the TARDIS on one of the fragments of the beacon.
^† Episode is missing This serial was written as a replacement for The Dream Spinner by Paul Wheeler, which for technical reasons was dropped at a late stage in production.
Patrick Troughton, Frazer Hines and Wendy Padbury were all away on location filming The War Games during the production of episode six and appear only in pre-filmed inserts.
While part 1 of the Third Doctor story The Mind of Evil is missing its authentic colour image data, it still has complete video, even if only available in either monochrome (on VHS) or manually colourised form (on DVD and Blu-ray).