Frances McCausland is a brilliant and level-headed girl who has started high school a year early. As soon as odd things happen in her town of Middleberg that an older boy named Larry Houdini - who turns out to be her little brother's imaginary friend - tells her those are mischieves of a Boogeyman for which she is framed. Frances soon realizes that Larry is the only one that can help her track down and stop the scary guy.