In February 1950, a Convair B-36 bomber, the largest in the world, takes off from Alaska carrying a Mark IV nuclear weapon on a secret Cold War training mission. Three engines catch fire over Canada's west coast, forcing the crew to jettison the bomb, bail out, and send the crippled aircraft on autopilot out over the Pacific. The US Air Force launches its largest search and rescue operation to that date, but the plane, five crewmen, and the bomb are never recovered. This film follows historians and investigators piecing together declassified documents, wreckage reports, and eyewitness accounts to reconstruct what happened and where the weapon might still lie. Interviews and archival footage cover the political panic over a live nuclear device sitting somewhere off the Canadian coast during the height of the Cold War, and the decades-long effort to locate the wreckage on Vancouver's Mount Kologet, where parts of the aircraft were eventually found. The bomb itself remains missing.