Bob, the station porter at Whatmidwell Station, discovers a dog hiding in some crates and adopts it as the station mascot in order to impress Harriet, the new teacher at the Orphanage. Station Jim, as he is named, soon proves his worth. From chasing moles off Stationmaster Pope's garden, alerting Bob to the fire at the Orphanage, to becoming an invaluable friend to young Henry, who dreams of a train coming to take him home.