Blood Truth by J. R. Ward

As a trainee in the Black Dagger Brotherhood's program, Boone has triumphed as a soldier and now fights side by side with the Brothers. Following his sire's unexpected death, he is taken off rotation against his protests--and he finds himself working with Butch O'Neal, former homicide cop, to catch a serial killer: Someone is targeting females of the species at a live action role play club. When the Brotherhood is called in to help, Boone insists on being a part of the effort--and the last thing he expects is to meet an enticing, mysterious female...who changes his life forever.

Ever since her sister was murdered at the club, Helaine has been committed to finding the killer, no matter the danger she faces. When she crosses paths with Boone, she doesn't know whether to trust him or not--and then she has no choice. As she herself becomes a target, and someone close to the Brotherhood is identified as the prime suspect, the two must work to together to solve the mystery...before it's too late. Will a madman come between the lovers or will true love and goodness triumph over a very mortal evil?

This book is part of the "Black Dagger Legacy" series.
Here are some other books from this series: