An alien demi-lizard in the future dispatches Blue Man Group androids to kidnap Peri, while exiling non-conformist subjects to 19th century Scotland
On the planet Karfel, the despotic Borad rules the population of roughly 500 with an iron fist, forcing them to obey his every whim or face excommunication by way of the titular Timelash, a corridor through space and time that leads to almost certain death. Using political proxies and a TV avatar, Borad rules from the shadows and is not even above cutting off the grain supply to the neighbouring planet of Banderel. His hate-fuelled rule in turn fuels rebellion, however, and thus both in the Karfel high council and in the easily accessible caves not-below-but-sort-of-adjacent-to the main/only dwelling on the planet, a band of freedom fighters are forming a loose set of principles that vaguely amount to a plan.
Meanwhile, The Sixth Doctor and Peri are gaily travelling in the TARDIS when they get stuck in said time corridor, nearly buy the proverbial space farm, and even witness a Karfel rebel swooshing through spacetime, untethered from reality. Steering their way to the relative safety of Karfel, they soon become embroiled in the political goings-on and are forced to pick a side. Unsurprisingly, they pick the underdog. Slightly surprisingly, they are also joined by 19th century Earthling, Herbert, on their quest for justice. The pressure is on, though. Giant dragon creatures lurk in the caves, blue-faced androids roam inevitable corridors, and the Bandrils of Banderel are preparing an attack.