Thirteen-year-old Stewart is academically brilliant but socially clueless. Fourteen-year-old Ashley is the undisputed "It" girl in her class, but her grades stink. Their worlds are about to collide when Stewart and his dad move in with Ashley and her mom. Stewart is trying to be 89.9 percent happy about it, but Ashley is 110 percent horrified. She already has to hide the real reason her dad moved out; "Spewart" could further threaten her position at the top of the social ladder. They are complete opposites. And yet, they have one thing in common: they -- like everyone else -- are made of molecules.