Responding to Dr. Saotome's request to search for the missing deep-sea research vessel Bathyscaphe, the Getter Team sets out and encounters a giant monster in the ocean. This creature is none other than Dragonosaurus, the culprit that sank the Bathyscaphe and has been attacking ships one after another. 　　 To defeat the threatening great sea beast, a "Robot Army" is hastily assembled, consisting of Grendizer, Great Mazinger, and Getter Robo G, along with Double Spazer, Venus A, and Dianan A. However, Boss Borot, who was left out of the group and rushed ahead in a reckless bid for glory, gets swallowed by Dragonosaurus, making it impossible to attack carelessly. Can the Robot Army overcome the formidable foe Dragonosaurus?