An industrial spy gets aboard the Endeavour to photograph the top secret equipment, but he turns out to be not such a bad bloke when he realises his methods endanger Captain King's life.

The Minus Five team discover a murdered man in Barrier Reef waters, and he is buried on a small, lonely island. He is to be exhumed by the police, but when Sgt. Davies goes to the grave the body is missing, and the Minus Five team land in a strange network of intrigue.

Two nuns ask the Minus Five team to help them recover a sacred chalice lost in a wreck off the Great Barrier Reef, but Captain Ted King reluctantly declines assistance as the Endeavour is under orders for another assignment. The nuns risk their lives when they decide to attempt the salvage job themselves.