Magnum is called back to Naval service by Admiral Hawkes, who has reason to suspect that there is a security leak at his Naval base that is leaking coded information, but can't ask any of his personnel to investigate for any one of them could be the ""mole"" behind the breach. He needs Magnum to root out the mole and plug the leak within three days, when he is due to receive some important submarine manuals written in code, which could be potentially very dangerous if they got into the wrong hands. Thomas' prime suspect is the fiancée of the Admiral's son, but when some stolen classified information is planted in his car, he himself accused of espionage...