Bound in Darkness by J.L. Weir

Silas never expected that taking Jadis as his mate would cause her to turn into the powerful hybrid known as a Dhamphyr. He quickly realizes he will have no choice but to face the gravity of the situation when reality strikes a vein. Word spreads that the mythical Dhamphyr exists, and Abigor – lord of the Bulgarian underworld – captures Silas, Jadis, and Dante. As the trio fight for their lives, Jadis finds that a swift death would be more forgiving than the heart wrenching choice Abigor forces her to make.