The President of the United States is visiting a new underwater installation when a power interruption freezes all communication. To complicate the situation they discover there is some sort of beam weapon stopping any of the safety over-ride mechanisms from activating.

Nelson and the Seaview witness the detonation of a new bomb developed by the Chinese. No bigger than a milk carton, it creates a blast 20 miles across. An American scientist who had defected to the other side steals it for his use.