Len Merrick believes his duty as a federal marshal is to bring prisoners in to face a fair trial, even if it costs him his own life. Merrick is impartial in the execution of that duty and courageous when facing down injustice. But he's also starting to feel his age, and he hopes a tall, dark-haired cowboy is willing to take his place.
Len Merrick is trying to keep order in a territory where men are willing to take the law into their own hands. Just such a case is about to play out as he rides up on a lynch mob preparing to hang a crusty old homesteader, named Pop Keith, whom they have accused of rustling and murder. Merrick demands that Pop be handed over to the law. When threatened, Merrick stands his ground, unflinchingly telling his friend Cheyenne Bodie and his deputy Lou Gray that if he is killed their duty is still the same: to bring the prisoner in to face a fair trial in Santa Loma.
Pop is handed over by cooler-headed men and Merrick leads the group back to Pop's homestead where he's nearly bushwhacked by the old coot's daughter, Mary. Merrick helps Pop fill out his Last Will and Testament while he has Bodie keep an eye on the feisty Mary.Later, Merrick makes a dangerous decision to ride through the desert to avoid the mob and get Pop to Santa Loma alive. During a break on the trail, Merrick tries to convince Bodie that he's the perfect candidate to succeed him as marshal, but Bodie turns him down. Later, the group is nearly overtaken by the mob and Merrick and his men take cover in some rocks. When one of the mob tries to get behind them, Bodie rushes off after him. While he's gone, Merrick is shot and mortally wounded.
After Bodie returns with a prisoner and sees his mentor badly hurt, Merrick speaks to him alone. He deputizes Cheyenne and makes him swear to get Pop to Santa Loma alive to face trial. Bodie agrees and then Merrick dies. After he's buried, Bodie spends a long time at the grave side and in eulogy tells Mary, "I've drifted all over the West, met a lot of men, but nobody like him. I only knew him maybe six months. It was like knowing him all my life. I never met a better man."