Everything is happening on the Narrow Gauge Railway. There is the new Controller, Mr. Percival, and there is the new locomotive, Mighty Mac. But this is no ordinary locomotive; in fact it has not one smokebox but two! At one end there is Mighty and at the other, Mac. On their first job they already start fighting, and in this case, over which way they should go to reach the proposed destination. Will they be able to reach a resolution, to work as one?