Emmy Budd is a twelve-year-old tomboy who finds her adventurer's match in the new boy in town, T.J. Blake. It is a hot summer day in the small Mid-Western hamlet of Jerseyville, Ohio. With no money and lots of time on their hands, Emmy and T.J. ferret out every freebie in town, from sailing kites off the tower in the local stadium to building a raft out of discarded lumber and sailing the old swimming hole. Emmy and T.J. sneak aboard a mail train bound for Pittsburgh and end up in the middle of a hijacking. Operating undercover, the teen detectives risk their lives as they confront a desperate fugitive.