"Fortress Fishhook" builds a military base on the sea bed. A demolition charge kills fish. The Sponge Man is outraged and destroys the site. (The Sponge Man was once a man, but he's lived so long underwater he's forgotten, as seen in COTU 47). The Sea Devils attack the Sponge with spear guns. The Sponge grabs Judy, tries to remember a girl's face, and releases her. Admiral Hutton calls in the Challengers. Their first meeting with the Sea Devils is a disaster: Judy flirts with Ace to goad Dane, and Biff and Rocky butt heads. The Challs insist on reasoning with Miklos, and climb a crane to talk. But the Sponge crushes it. The Sea Devils' giant robot Neptimus rises to fight, but the Sponge absorbs heat and freezes the robot's gears. Strike one... Meanwhile, a sinister cabal named Scorpio gloats. They were paid to sabotage Fortress Fishhook, and the Sponge does it for them. One member is Lisa, Miklos's old neighbor. She'll get close... The Sponge rampages, absorbing all sound. Using sign language, the Challs commandeer a cable truck, rig a harpoon, and zap the Sponge with electricity. He's stuffed in a cell. Lisa feigns friendship and releases him. The Sea Devils blame the Challs, and the two groups brawl. Back to reality, Ace finds a button pointing to Lisa. Judy threatens to cut off her hair! and Lisa spills the beans. Mixed teams chase the Sponge and Scorpio. One team raids Scorpio HQ as they launch a missile full of poison gas! The Sponge catches the missile - and it goes off! Poison gas spills on the wind. The only one who can absorb it is the Sponge, and he's reverting to human! Still, Miklos can't let the gas hurt anyone, and sucks it into his body. In agony he climbs a water tower and falls in, neutralizing the poison. His sacrifice saved the city. "Like a sponge, he wiped his slate clean."

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