Old Harry tells Steve Gabo about two million dollars of gold coin carried on a plane lost during World War 2, which he has been trying to locate for years. The Minus Five team begin a search and find more than they bargained for - two skeletons, and two armed men who could be murderers, but who are in fact Commonwealth Police.

Exploring an underwater oil field near the Great Barrier Reef, the mini-submarine crew strikes new danger - an ear-splitting, high-frequency sound that kills fish, and even disables the Minus Five electronic equipment,