Blood vow - J. R. Ward

A tough vampire warrior in training and a quick-witted aristocrat
develop an irresistible attraction and work together to uncover a
mystery. The second in a new spin-off paranormal romance series set in
the world of the #1 New York Times bestselling Black Dagger Brotherhood.

Trainees
at the Black Dagger Brotherhood' training centre continue to prepare
for the fight against the Lessening Society, but fighting is the last
thing on Axe's mind. Still plagued with the guilt of his father's death,
the brooding loner finds himself battling an unlikely attraction to
Peyton's bright, aristocratic cousin, Elise.

Elise feels it too -
and when the two are thrown together in unusual circumstances Elise
must decide whether she can trust Axe to help her uncover the mystery
surrounding her sister's death.

Meanwhile, Mary and Rhage are in
the process of adopting Bitty, a young pretrans orphan, until the
appearance of a young male claiming to be Bitty's blooded uncle
threatens to tear the new family apart.