The Last Stratiote — Leann Neal Reilly

She carries a novel virus in her blood. One that rages against a peculiar parasite curled in her heart. Foul-mouthed and bloodthirsty, Elira Dukagjini should have died 500 hundred years ago. Instead she left her Albanian homeland at the start of the 16th century to fight as a stratiote, a mercenary. She wears a gruesome keepsake in a leather pouch around her neck and a telltale scar on her breast. Driven to enforce the primal Blood Law, Elira spends her days running a café and bookstore in a modern Boston suburb while hunting human prey at night. Until one fateful night when the prey Elira hunts have their own prey: Mirjeta Gjakova, the intended honor sacrifice of fundamentalist imam Xhemajl Krasniqi --  Elira's uncanny and more civilized twin living the life that Elira never had. The war that Elira left behind in the Balkans never really ended. And now, in the 21st Century, she once again must choose between slaking her endless bloodthirst and finally quenching it.