Prairie Song by Cheryl Anne Porter

A desperate bargain
Running for her life, Kate Chandler flees to Oklahoma with a price on her head, hoping to stake a claim in the Great Land Run of 1889. But with no money, no protection, no food--and an unborn baby to think about--she is desperate enough to accept a devil's bargain from notorious bounty hunter Cole Youngblood. Ruggedly handsome, he'll stake her claim if she'll be a mother to his sister's three orphaned children--unaware of Kate's dangerous secret: she is the quarry he's been hired to find.

A dangerous love
Cole knows Kate is running from something terrible; the fear in her eyes is clear as day. But that doesn't change his plan to marry her, make the Land Run, then leave Kate and the children behind--safe away from the hard life he's chosen. He didn't expect the wild emotions that would sear his hardened heart and make him yearn for a life beyond the grim realities of living by his gun. But as passion exposes the deadly secrets that shadow them both, he knows their only hope for a future together is to forge a love stronger than the danger trying to tear them apart.