Teen skater Ken Park (nicknamed Krap Nek; his name spelled and pronounced backward) kills himself at a Visalia skate park; his death bookends the lives of four other young people who knew him: Shawn, the most conventional; Tate brims with psychotic rage; Claude is habitually harassed by his brutish father and coddled, rather uncomfortably, by his enormously pregnant mother; and Peaches looks after her devoutly religious father, but yearns for freedom. They're all rather tight, or so they claim.

Three young boys, Rocky, Colt and Tum Tum together with their neighbor girl, computer whiz Amanda are visiting Mega Mountain amusement park when it is invaded by an army of ninjas led by evil Medusa, who wants to take over the park and hold the owners for ransom. Kids and retired TV star Dave Dragon, who made his farewell appearance at the park at the time the ninjas appeared, have to break Medusa's vicious plans.