Dr. Lo has developed a growth ray that he uses to enlarge sea creatures and threaten underwater cities. Jabberjaw and the gang soon find themselves battling the evil Doctor and his creations.

Commander Dumax and his army of praying manti (who look exactly like Space Ghost's sidekick Zorak) have come to invade Earth. The Neptune's, on their way to Hydrostan, hear of a UFO sighting in the area ,and Biff decides to use this as a publicity stunt. Unfortunately, Clamhead and Jabberjaw are pursued by the aliens, the stunt backfires. In the meantime, Dumax gets an Earth identification device, which will help with his plans. The Neptune's are taken prisoner by Dumax but escape and must thwart his invasion plans.

In Oysteralia, spy ring leader Maximus and his assistant, Dr. Chemo, have built the world's most powerful robot, which they plan to use to transfer microfilm containing their spy roster. The Neptune's arrive in Oysteralia to play at the Olympic Village during the 2076 Underwater Olympics. Jabberjaw accidentally obtains and then swallows the microfilm canister, putting his life in danger. He and the robot enter the underwater obstacle course race, where he can make contact with the agent known as ""X.""

Atlantis Prime Minister Dorsal executes a mock attack against his city to convince Queen Atlanta to allow him to attack other underwater cities. His goal is to conquer all of the other cities and then overthrow Altanta, making emperor of the undersea world. The Neptune's are accidentally ejected from the cruise ship where they are performing and are taken prisoner by Dorsal as invaders. They discover his plan and decide to inform Atlanta of his intentions.

A general arives in the port of Sao Mareno, the capital of Aquantina, with a disk for archeologist Dr. Acosta. The disk contains hieroglyphics showing the whereabouts of the ancient treasure of Panaqua. The treasure is guarded by Panaquan tribesmen, but because it is desired by the evil Octopus, the government wants to place it in the museum. Shelley gets the Neptunes to Pier 213 instead of 312 (for their trip to Aquapuclo), and they join Dr. Acosta on his quest. The Octopus, who drives a submarine shaped like a squid, with working tentacles, traps Acosta's ship, and Jabberjaw is ejected by the automatic trash ejector as Acosta's sub fills with water. Jabberjaw rejoins them in Acosta's aquavan (like an escape pod) but is later captured and duplicated by the Octopus, who obtains the disk, but not before an imprint that Acosta can use is left in Jabberjaw. The gang fights hostile tribesmen but find the computer left by a previous expedition, which leads them to the central pyramid in the

While participating in a rodeo at Aqualand, Jabberjaw sees Dr. Cybron's henchmen kidnap the Rajah, and replace him with a robot duplicate. He tells the Neptunes, and Cybron tries to silence them by sending a runaway stagecoach over a cliff. When that fails, he captures Bubbles, and sends a duplicate of her to capture the others. The group rescues Bubbles and the Rajah, and discovers that Dr. Cybron himself is a robot.

Biff books the group on a tanker to Amsteraqua after another gig falls through, this being the cheapest way to go straight there. The Piranha has designs on ruling the Underwater States of America and captures the tanker for its load of special rocket fuel. The Neptune's scuttle the Piranha's rocket practically dismantling the control center and messing with the rocket's fuel delivery system. Jabber manages to launch the rocket accidentally to a different destination, with its cargo of sleep dust.