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,

The Endeavour runs before Cyclone Ada, which devastates tourist resorts on the Great Barrier Reef and towns on the North Queensland coast. After the disaster, the Minus Five team return to the area to search for survivors, and play an important role in rescue work.