Nelson seems to have killed a Prof Mason. Nelson says Masons magnet to create energy affects the moon and if not stopped will destroy earth. Crane tries to go to Los Angeles to tell that he was with Nelson when the attack occured. But Crane is caught and when he shows up on TV denies that he was with Nelson. When Crane escapes and returns he finds out what happened. The Seaview leaves Santa Barbara with Crane forced to dive the sub to escape. Nelson comes aboard in a crate. Nelson watches a tape of the scene where he was framed for shooting Mason and catches a ring on the impostor. Many crew member turn out to be fakes telling Crane and Nelson somebody is aboard. The fake leaves a bomb and escapes in the Flying Sub as Crane. Nelson catches the impostor and it turns out to be Prof Mason. The Seaview reaches the magnets location and blows it up before it can get the Moon too close to earth.