This true story follows the exploits of a top secret British military mission to destroy Nazi radio ships in a neutral harbor during WWII. The daring plan is led by British Intelligence officers Col. Lewis Pugh (Gregory Peck) and Capt. Gavin Stewart (Roger Moore). Since the ships are in neutral territory the British Military command, while encouraging the scheme, must deny any knowledge of it if it fails. Pugh and Stewart enlist the aid of retired officer Col. Bill Grice (David Niven) and some of his former soldiers. On the pretext of being on a fishing expedition, these seemingly drunken old men in civilian clothing must board and destroy 3 Nazi ships, whose radio transmissions have resulted in Nazi submarines sinking allied ships. While Stewart arranges a diversion on shore, Pugh and Grice carry out the dangerous raid on and destruction of the Nazi ships.