The Endeavour is assigned by the government to chart unknown channels in the Barrier Reef. A man once badly mauled by a white pointer shark seeks revenge in the shark's breeding ground and endangers the lives of the Minus Five divers.

The Endeavour's attractive new scientist learns a bitter lesson in security when she innocently arranges passage to Townsville for a colleague. Customs officer Morgan and the Minus Five team are held at gunpoint by the passenger who demands the surrender of counterfeit money plates which have been discovered attached to the ship's hull.