Frontier Earth: Searcher — Bruce Boxleitner

The year is 1882. The enigmatic gunman known as Macklin has made a home for himself in Tombstone, Arizona. As his memory teens, he has come to realize that he is not human, but a being from another planet, sent to protect Earth from a coming invasion by another alien species. Still, he has many questions--about his enemies, about himself--and believes he can find some answers in Tucson, where another of his kind lives.

But during his search he is drawn into the conflict that rages to the mountains outside of Tucson, between the men who mine far silver and the Apaches who hold the mountains sacred. Caught in the middle of a human war, Macklin must not forget that while he has been hunting for the truth, something continues to hunt him. Something not of this Earth .. .