The tracer detects the second segment on the planet Calufrax. The TARDIS makes a bumpy landing, and the Doctor and Romana soon discover that they are not on Calufrax at all. They are in fact on Zanak, a planet that has...展开been hollowed out and fitted with engines so that it can transmat through space and materialise around others - such as Calufrax - to plunder their mineral wealth, leaving them as shrunken husks held by gravitational forces in a 'trophy room'.
Ostensibly in charge is the Captain, whose body has been partially replaced with robotic parts following a near-fatal crash, but he is merely a puppet controlled by his nurse - a projection of Zanak's original ruler, the aged Queen Xanxia.
Xanxia is using time dams, powered by the forces generated in the trophy room, to keep her body alive until this new, younger form has stabilised. The Captain prepares Zanak to 'jump' again - this time with Earth as its target.
The Doctor attempts to thwart his plans, calling on the assistance of the Mentiads - a gestalt of telepaths amongst Zanak's indigenous population - to sabotage the engines.
The Captain rebels against the nurse, but she kills him. The nurse herself is then destroyed by one of the Zanak natives whom the Doctor, Romana and K9 have befriended.
The Doctor realises that the second segment comprises the whole of the planet Calufrax. He contrives to drop the compressed husks from the trophy room into a space-time vortex created by the TARDIS in the centre of Zanak, and is then able to pick up and convert the segment at his leisure.