Thirteen-year-old Sully Stringfellow, his arch-nemesis Izzy Cisco, friend Moleman, and a league of long-forgotten plumber heroes team up to save Nitro City from mutant creatures in the sewers.

When Gran and his family move to Carousel, he has no idea that the town is built atop a secret. Little does he suspect, as he walks his sister to school or casually eats a banana, that mysterious forces lurk mere inches beneath his feet, tearing up the earth like mini-hurricanes and causing the town to slowly but surely sink. When Gran's friend, the difficult-to-impress Catalina Catalan, presses a silver handle into a hillside and opens a doorway...