When HMAS Hammersley runs into a submerged buoy equipped with a sophisticated transponder unit, two crew members narrowly escape death and the ship gets involved in a hunt for a murderous gang of drug smugglers.
On the way to drop Australian Federal Police Agents Greg Murphy and Alicia Turnball on Bright Island, scene of the suspicious death by poisoning of marine biologist Dr Lisa Holmes, Hammersley runs over a submerged buoy.
Investigating, ship’s diver ET finds that the buoy is attached to a mysterious metal case and contains a transponder unit emitting a high-powered signal. Ordered to proceed on her original mission, Hammersley drops off the Federal Agents on Bright Island, only to discover the presence there of Dr Ursula Morrell, the beautiful CEO of the company for which Lisa Holmes worked.
Executive Officer Lieutenant Kate McGregor becomes aware of the strong chemistry between Ursula and Hammersley’s Commanding Officer Lieutenant Commander Mike Flynn, a man Kate once herself loved and lost. Hammersley then returns to the mystery buoy, which turns out to be booby-trapped, almost killing crew members Swain and ET. Hammersley now goes after the perpetrators, apprehends them and takes them back to Base. The successful patrol completed, Kate discovers Ursula Morrell is there to meet Mike. Obviously the attraction between them has progressed another stage.