 In the North Atlantic, after sinking a British freighter and its occupied lifeboats, the cruel and arrogant Altberg commands his U-boat to submerge, surfacing later to find the dead body of a seaman who died clinging to the exterior railing of the sub.A search of the body reveals a strange piece of carved ivory.Because of its apparent great age and value, one of Altberg's officers keeps the object, and shortly thereafter, strange phenomena begin to occur - such as the dead man apparently swimming away rather than sinking.