"Do not let a mop sit overnight in water. Fix things before they get too big for fixing." Fifth-grader Mattie Breen writes it all down. She has just one week to convince Uncle Potluck to take her on as his custodial apprentice before school starts. As his apprentice, she'll have important work to do during lunch and recess . . . work that will keep her safely away from other fifth-graders. But when Mattie's plans come crashing down, she ends up with a friend who is hound dog true.