When the Fat Controller sends Thomas to work at the Blue Mountain Quarry, Thomas spots an engine he has never seen before trying to hide. Determined to get to the bottom of the mystery, Thomas tracks down and befriends Luke, who tells Thomas he is hiding because he did something so bad, he could be sent away from the Island of Sodor forever. Thomas does not believe this and sets off on a journey to discover the truth behind the story of the poor runaway engine.