Ten Cents delivers his last cargo barge to the Old Quay after a very busy day. As night falls, it is towed away by a mysterious boat. Captain Star is cross to hear that one of his customer's deliveries is missing and puts Ten Cents on dredger detail - not a pleasant task. But Grampus, a small submarine, sees another barge being stolen at night, so Captain Star and Captain Zero join forces to find the thief....