A bizarre attempted murder by the Mafia can only be prevented by a marine biologist and the Minus Five team working together. They must catch a deadly stone fish alive so that an antidote can then be made to save the dying man.

An ageing sea captain who was the original skipper of the Endeavour determines to scuttle the ship so they can die together. Alone with him on the ship, Tracey Deane tries to change his mind.

One of the Minus Five team acts as bait to catch a company official selling classified information about a newly discovered nickel field on the Barrier Reef.