Arriving on horseback at a railroad watering station where he means to briefly rest and hopefully find some refreshment before moving on, Lone McGantry tangles with a pair of rowdy cowboys who are up to no good.

No sooner is that resolved than a train arrives after having been just robbed. Aboard is Jeth Howard, an old friend of Lone's from his days as an army scout. As a favor to Jeth, who has particular reasons for wanting to regain a priceless heirloom in the form of a jeweled brooch that was taken during the robbery, Lone agrees to aid him in the pursuit.

The pair proceed to chase the train robbers-the notorious Dar Pierce gang-through Colorado and across the borderlands of Nebraska and Kansas. Along the way they encounter other dangers, including betrayal, a near lynching, and the rescue of Minowi, an Indian girl on the run, before the final showdown comes in Massacre Canyon, where an historic Indian battle once took place.