Unlike his perfect older sister, Conner hates piano lessons and gets bad grades at math. He loves animals, but his parents have a no-pets rule. When the local animal shelter gets over-crowded, everone in Conner's animal club agrees to take in a foster pet. Although he'd much rather have a dog, Conner takes home Oscar, the rat, and while keeping Oscar hidden, discovers there is more to rats than he expected. But what will Conner's family think if they find out about Oscar?