It all began on a summer night aboard a cruise ship with Jun and Ippei. Yuriko first sees a UFO, then finds a strange doll on deck. The doll identifies herself as Zerni, a member of an alien race, and reveals that a violent monster's egg has fallen into the sea. Jun and Ippei don't believe Yuriko until they speak with Zerni themselves. Zerni explains that the monster must be hunted down.

The "Sea of Death" causes five separate ship disasters. A giant octopus consumes a Japanese fishing vessel and sends the crew to their deaths. Sudar, Jun and Ippei find out that Minami, Yuzo and Anita are about to be executed for blaspheming the monster. At the last minute, they are saved when the beast's lair is destroyed by aerial bombing. The wounded beast lashes out at the village.