The Sub-Humans, giant green hammer-headed monsters, rampage across the city. The Challengers zoom low in the Gallopin' Gizmo and get caught, except the Gizmo blows into four flying parts... Under the sea, in the mobile Villo's Villa, Villo and Brainex watch the battle. Villo insists on killing the Challs, so Brainex makes them vanish. A call comes in: Bubble-Master wants an interview! The starstruck young villain blasts bubbles from his bubble gun. Villo sends him out as a distraction. Bubble-Master busts a jewelry store, then flattens and drenches the Challs with bubbles... The Villa walks ashore. Bubble-Master worships Villo, but gushes about "our" plans. In BM's bubble-craft, the two make the Gizmo spin out of control - then Villo kicks BM out! The newbie admires Villo's villainy as he floats on a bubble-chute... Next Brainex double-crosses Villo and walks the HQ back into the ocean. Laughing, the Challs bounce Villo and jail him. Villo even spills that the Sub-Humans are "creations of calculus"... Brainex, out to prove his superiority, sends the Sub-Humans to wreck an amusement park. The Challs can't dent them, and Red breaks an arm... Villo gets sprung by Bubble-Master's torch-bubble... Needing super-calculus, Prof mans a giant college computer and runs counter-equations. The Sub-Humans explode... Defeated, Brainex recalls Villo and Bubble-Master, and all three make new plans.

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