Diesel Express is set in an alternative time period of post-WW2, begins after a ceasefire that leads the war to an end in 1953. The war took longer than predictions. Nuclear attacks completely changed the earth's climate. Nature is beyond any chance of recovery.

While cities are guarded by walls, outland is under control by a doomsday cult which is led by a stranger man named Marius. As an individualist, Marius convinces groups to act against the cities. His idea spread quickly because of the post war conjunctures.

The only transportation way being used between the cities is railroad. All the resource trade is made with highly armored diesel trains called "The Dreadnought"s. Our character takes his place in a dreadnought by joining the "regiment".