After a fatal car crash in Lordsburg, New Mexico, investigators find a mysterious machine component that they turn over to the nearby Los Alamos National Laboratory for identification. Scientists there declare that it is one component of an advanced portable nuclear weapon designed by an unknown, presumably hostile power. The discovery prompts Paul Reagan (Richard Denning), chief of the Security Investigation Division (SID), to send agent John Williams (John Ireland (actor)) to investigate the source of these components and to prevent them from being assembled into a functioning weapon. As more parts are smuggled into the United States, the investigation expands and a pattern begins to emerge which points to Marseilles, France.