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.

Word comes through that Dr Liscomb has been kidnapped by a foreign agent posing as a toy importer. Liscomb has cracked the secret of the X factor, a new ingredient and everyone wants it.