In the summer of 1872 a deadly pistolero, Brett Dalton, is hired to assassinate President Ulysses S. Grant as he embarks on a re-election campaign across the western states. The president will be travelling via the Union Pacific Railroad, and when his locomotive stops to take on water at an isolated pumping station on the Nebraska/Wyoming border the lethal plot will be launched. With hostile Sioux Indians also planning to attack the train, it is up to Thaddeus McEvoy, a special investigator in the newly formed Department of Justice, to save Grant's life. With Widower, Tatum Barklam, and his beautiful daughter, Sarah, are used to a predictable life at the pumping station, but they are about to experience a very different pace when Dalton and his gang of desperadoes come thundering into their lives.