When a rocket with six nuclear bombs was sent into outer space for development of the planet Jupiter, the rocket malfunctions and lands into the sea, with only one of the bombs exploding, causing a disaster at sea. With four of the bombs recovered, it's up to the Science Patrol to find the missing bomb. Meanwhile, Fuji is given a vacation by Capt. Muramatsu (much to Ide's jealousy), and she, Hoshino and a little girl named Michiko go to the seaside Mamiyama Hotel and have fun. Meanwhile, Hayata investigates a boat disaster caused by a moving wake in the sea, caused by the giant humanoid sea monster Ragon. This is not the gentle beast as seen in Ultra Q, this Ragon, mutated by the radiation of the aforementioned exploded bomb, is hostile and violent. Not only is it heading towards the Mamiyama Hotel, but the missing bomb is dangling from its body!!! Will Fuji and the two children be safe? Can Ultraman fight Ragon without detonating the atomic bomb?