Casper, Johnny, and Gwinny are sure they'll never be happy again when their mother marries Jack, who is as mean as an ogre. To make matters worse, two obnoxious stepbrothers, Malcolm and Douglas, move in as well. No one -- except the parents -- seems happy. But when Jack gives a chemistry set to each group of kids, bigger problems take over. These are, it turns out, not your average chemicals. In one hilarious experiment after another, the kids discover they can fly, switch bodies with one another, and even disappear. If only they could figure out how to undo all of this Are one combustible stepfamily and two explosive chemistry sets a formula for disaster?