The Doctor's rather manic attempts to refamiliarise himself with the workings of the TARDIS result in the crew finding themselves stranded on an extremely inhospitable planet, as the TARDIS sinks through the cracking ice it landed on. This is Endpoint, the last planet in a crumbled galaxy, where hairless post-humans scrape out an existence on the noxious, barely habitable surface. In their efforts to persuade someone to resurrect the TARDIS, they encounter the real power on Endpoint, a cyborg named Silver, whose enhanced capabilities and mastery of technology mean he dictates what really happens, not only in the capital city, Hope, but on the entire planet. But he is worried: there is something going on that is beyond even his control. In increasing numbers, people are being killed on the streets of Hope. As the Doctor investigates, he discovers a hidden community below the surface of Endpoint, who are desperate enough to kill...