Tom Derry owed Buck Rainey his life—twice over.
When Rainey saved him from an angry bull, Tom thought that here was a good and brave man. When Rainey helped him fight some men who wanted his blood, Tom knew that if there was ever anything he could do for Buck, he'd do it gladly.
Rainey knew this too. So he asked Tom to help get his friend Barry Christian out of jail—and out of a hanging. Tom figured that if Christian was Buck's friend, he couldn't be a murderer. And when Buck said the Jim Silver, the man who'd put Christian behind bars, was a lying, scheming killer, Tom had no reason to doubt him.
So Tom helped Christian escape—and was repaid by being sent on a ride on Christian's horse, the horse whose trail Silver was tracking. When Silver caught up with him, Tom though that he was finished. But Jim Silver knew a decent man when he saw one, and let Derry go. It was then that Tom realized the truth: Christian was a killer, and if he had the chance, he would kill Silver. Tom knew he had to stop him somehow—even if it meant doublecrossing the man who had twice saved his life.