It is the height of the Napoleonic Wars and, at sea, Capt. Crawford (Alec Guinness) is in charge of the H.M.S. Defiant. Well-liked by his crew, Crawford clashes with the newest man on board, Lt. Scott-Padget (Dirk Bogarde). Scott-Padget thinks Crawford is soft on the men and uses Crawford's son, who is aboard, to manipulate the ship's leader. As tensions on the vessel mount, Crawford must keep his sailors focused on fighting the enemy, not each other.