Eve of Destruction(2009)

Sylvia Day

For Evangeline Hollis, a scorching one-night stand has led to a divine punishment--the Mark of Cain.
Now reunited, Eve and Cain are working on transitioning their insatiable desire into a tentative new relationship even as she struggles to become a full-fledged Mark--one of thousands of sinners forced to hunt demons as penance. When her training class goes on a field trip to an abandoned military base, things take a dark turn: There's a demon hidden among them, killing off Eve's classmates one by one.

To make a bad situation more dangerous, Eve's body is still adapting to the Mark and the new abilities and challenges that came with it--such as uncontrollable bloodlust...which seems to be inciting another kind of lust altogether.

With Cain out on assignment, Eve's simmering attraction to his equally sexy brother Abel grows--and Abel is more than willing to take the heat...