Night of the Comancheros — Lauren Paine

Ann Carruthers has no idea what searching for her brother in the wild New Mexico Territory will mean. But what else can a girl, even an English girl not much past twenty, do when her brother vanishes? How can she know that bandits, Indians, and violence are things people in the territory live with every day? Ann doesn't realize how much danger she is in until the son of a Comanche chief offers one hundred horses for her. To save herself she has to pretend to belong to John Hardisty. Sure, he is a loner and a hardcase, but he can ride, shoot, and fight. And he is her one chance of survival in the lawless wilderness.