In the aftermath of a devastating German U-boat attack during World War II, one of the few survivors, Irishman Murphy, is left stranded in a remote river region of South America. With his ship destroyed and crewmates killed, Murphy vows vengeance against the enemy submarine. Resourceful and determined, he finds refuge with a French engineer living on a torpedoed tanker. Together, they repair a derelict floatplane. In his single-minded quest for retribution, Murphy is sometimes at odds with the local mission doctor, who advocates for peace over further violence. Determined yet isolated, Murphy's relentless pursuit of the U-boat becomes an obsession.

Murphy repeatedly attempts to launch his attacks independently, often facing harsh natural obstacles and the shadowy presence of the surviving U-boat crew. As tensions rise, he risks not only his life but also the lives of those around him, as he blurs the line between resolute heroism and reckless vengeance. His journey thrusts him into confrontations both external and internal, testing his character and resolve at every turn. Meanwhile, the stakes continue to escalate under the backdrop of an exotic and dangerous landscape. Murphy’s steadfast mission unfolds into a gripping tale of perseverance, testing the limits of justice and revenge in the face of wartime horrors.