Advanced space-humans and alien invaders go head-to-head in Tombstone, Arizona, in 1881. (western fans will exclaim, Aha!) Macklin and Doris are descendants of the lost Roanoke colony, some of whom were rescued and taken into space by benevolent aliens of the multispecies Associative. As Monitors, they keep an eye on Earth, but when the predatory alien Kra’agh attack their ship, they crash, separately, on Earth. His memory lost, Macklin wanders into Tombstone, where he finds a room at the boardinghouse of kindly and attractive widow Sarah Nevers. Inevitably, he gets mixed up with the Earp brothers and their allies. Meanwhile, the two ghastly Kra’agh hunters (they can eat terrestrial life-forms and feed on pain and fear) kill some humans, absorb the contents of their brains, disguise themselves with projected illusions, and creep in pursuit. Naturally, they side with the Clanton gang. Doris finally catches up with Macklin and helps him remember what’s going on, but his intelligent Companion is damaged and requires rare elements for repair. The Kra’agh, however, have destroyed the Monitors’ Moon base and are poised to invade Earth. They try to trap Macklin at the OK Corral, playing their part in the historic shootout, then attack the boardinghouse and grab Sarah. Doris will attempt to rendezvous with an emergency pickup craft, while Macklin follows poor Sarah. First-novelist/actor Boxleitner (the Babylon 5 series, etc.) gives this oft-exploited scenario an organized, crisply delivered, and well-informed workout. Expect sequels.