For his birthday, Casey Alexander's mother packs him a lunch full of some of his favorite foods. When the lunch bell sounds, he heads over to the cabinet where the lunches are kept and finds the empty bag on the floor. As the other kids grab their lunches, Casey sets out to find who stole his lunch and to expose the thief so no one else has their lunch stolen in the future. Along the way, he finds a variety of clues that keep pointing him to the culprit and is surprised to find out the truth.