Summer vacation is almost here! And Pea O'Neil is stoked to try out the new local BMX track which is finally open. He and his gang of friends can ride all summer long!

But when Pea tries a back flip, he unwittingly opens a portal to another dimension and hordes of flying mutant zombie rats are unleashed upon the city. With the help of an otherworldly talking cat sent to help prevent the demise of humankind, Pea and his friends must hunt down the hungry mutants and send them back before the portal closes.

But when the zombie rats attack a neighbor man, the boys have to enlist the help of a graveyard looney and the city's stray cats. With time running out, Pea and his gang track the monsters to the city's sewer system. But in the city sewer of Milwaukee, Wisconsin, it's eat...or get eaten.