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.

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.