Guns of the Alamo / Bradford Scott.

Originally published in 1960.

Walt Slade, ace lieutenant of the Texas Rangers, is the man most feared by the owlhoots and drygulchers of the old Texas Border. The sight of this tall lawman with the lightning-fast draw astride his great black horse, Shadow, symbolizes defense of the innocent and the end of reckless careers of lawlessness. Walt travels undercover, keeping his Ranger status a secret. To many, he is known as El Halcon and believed to be an owlhoot who is too good at what he does to be caught. One hour in San Antonio and Slade had: stopped a deadly attack, saved a beautiful girl's life, and left three men dead. Half an hour later, the three dead men had disappeared and Slade was marked for murder, the target for a dozen or more vicious gunslingers, not one of whom he knew by sight. Slade had only planned to stop in San Antonio for a few days of rest after finishing a job on the Pecos River. Now he won't leave town until he has cleaned out all the troublemakers and stopped the snake that leads them for good.