Thirteen-year-old Stewart Inkster is academically brilliant but "ungifted" socially. Fourteen-year-old Ashley Anderson is the undisputed "It" girl of grade nine, but her marks stink. Their worlds are about to collide when Stewart and his dad move in with Ashley and her mom. "The Brady Bunch" it isn't. Stewart is trying to be 89.9% happy about it, but Ashley is 110% horrified. She already has to hide the truth behind her parents' divorce; "Spewart" could further threaten her position at the top of the social ladder. They are complete opposites. And yet, no matter their differences, they share one thing in common: they--like the rest of us--are all made of molecules.      Written in alternating voices, Susin Nielsen deftly explores family tragedy and family ties; sibling rivalry and union; and adolescent confusion and revelation.