When Zack's classmate Andrew, who always has a story to top everyone else's story, finally agrees to submit to a lie detector test at the police station, Andrew messes around with the lie detector machine and suddenly his butt grows every time he tells a lie! This may be easy to remedy for any other kid, but Andrew just can't help himself, and his butt grows so much, and so much MORE, that he may cause his and Zack's project for the science fair to be junk! How will Zack and his friends solve Andrew's growing problem?
