The Bootheel — Kevin Wolf

All fourteen-year-old Tyler ever wanted was to be a cowhand. Virgil Hutt, The Bootheel's owner, brought the orphan boy to the ranch and raised him like a son. Then Hutt sent for the outlaw Case Spencer, a grim-faced gunman like the men in the boy's dime novels. Together, Tyler and the gunman follow a treasure map into Old Mexico. When their grand adventure turns deadly, Tyler's last shreds of innocence tear away and Spencer finds that his redemption lies not in his dark past, but in protecting the young man's future.