Gibson Pardee, U.S.N.R. the Port Warden of Los Angeles harbor, runs his office with an iron hand and is unbending under his responsibilities. Marshall Walker, his close ex-Navy friend and assistant, confined to a wheel chair, is happy with his wife Kay and their two small children. As the two had always feared, they learn that a freighter that just docked has an atomic bomb aboard. The ship captain, Snyder, tells them that the bomb may be set off anytime within the next 12 hours by a Communist "detonating" ship hovering somewhere off shore. To prevent panic, Gibson and Walker get Gibson's enemy, tugboat captain Stanley Povich, to agree to tow the bomb-ship to sea in a race against time.