Having apparently reached a new destination - a space museum on the barren planet Xeros - the four travellers discover that the TARDIS has in fact 'jumped a time track', giving them a glimpse into their own future: a future in which they end up as static exhibits in museum display cases!

As time catches up with them, the Doctor and his companions have to try to avert this possible future by altering events in the present, never sure whether the steps they are taking will lead to their demise or their salvation. Fortunately they win through in the end, helping a group of youthful Xeron rebels (Peter Sanders, Peter Craze, Jeremy Bulloch, Bill Starkey, Michael Golden, Edward Granville, David Wolliscroft) to overthrow the warlike Morok invaders (Ivor Salter [Commander], Billy Cornelius, Lawrence Dean, Peter Diamond, Ken Norris, Salvin Stewart [Guards]), led by Governor Lobos (Richard Shaw), who have established the museum as a monument to their galactic conquests.

_{Synopsis from Doctor Who: The First Doctor Handbook by David J. Howe, Mark Stammers and Stephen James Walker, reprinted with permission; further reproduction is not permitted. Available from Telos}