The idea of icebergs in the tropical waters of the Barrier Reef at first amuses the Minus Five team, but the situation becomes grim when the icebergs prove to be real and a threat to shipping. Captain Ted King asks the inventor of the icebergs on board the Endeavour to join the team.

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.