Expo 2068

A newly produced core reactor is being transported to the Manicougan Power Complex, which is near enough found near the Atlantic Seaboard of North America, which the Mysterons have announced that they will submit a "heavy blow to the prestige of the world."
While conducting security checks within the designated area, it becomes aware that a missing, off route Transporter 43, which has already inadvertently crashed over the edge of a demolished bridge, thanks to Captain Black's deliberate diversion of the planned route, is what the Mysterons are using to smuggle the reactor.
With the core reactor already being aerially ferried in a shipping helicopter, and with the controller at the Expo 2068 construction site looking down at the barrel of Captain Black's hand-gun, Spectrum are back to square one before they can investigate the reactor situation.
It becomes apparent however, that the copter's target is the Expo 2068 site, and evidence confirms that the thermal safety valve has been removed from the reactor, with a rapidly descending countdown already initiated, and when zero approaches, the reactor will impend a nuclear explosion.