The TARDIS materialises in Iceworld, a space trading colony on the dark side of the planet Svartos. The Doctor and Mel encounter Glitz and learn that he has come here to search for a supposed treasure guarded by a dragon. Also on Svartos is Kane, a – literally – cold-blooded criminal who has been imprisoned here by his own people from the planet Proamon.
The Doctor and Mel, aided by Ace, a disaffected waitress, discover that the ‘dragon’ is a biomechanoid and the ‘treasure’ a power crystal held within its head. Kane is desperate to obtain the crystal and the Doctor uses it to bargain with him for Ace’s freedom. It turns out that Iceworld is a huge spacecraft and the crystal the key that Kane needs in order to activate it.