The British Merchant Navy hospital ship San Andreas is en route from Murmansk to Halifax, Nova Scotia during World War II. It is forced to change its destination to Aberdeen, Scotland. It belonged to the Liberty Ship class design with large red crosses painted on the sides of its hull, San Andreas should have immunity from attack from all sides in the war and be granted safe passage.

          The first sign of trouble occurs when the ship’s lights mysteriously fail just before a pre-dawn bombing attack that severely damages its superstructure and sinks its escort frigate. With most of the senior officers dead and the captain incapacitated, Bosun Archie McKinnon must take charge of the damaged ship and steer her to safety despite German aircraft, U-boats, stormy Arctic weather and sabotage by an unknown traitor on board. He must also discover the reason for the frantic and repeated German attempts to sink the San Andreas.