Watchers in the Night (The Guardians of the Night, Book 1)

the long version

Vampires. They hunt in every major city, hidden by the crowds, shielded by disbelief. They are Killers, and their prey is human. Not all vampires are Killers. The Guardians of the Night sacrifice the superior physical and psychic strength that comes with feeding on humans to protect them. But the Guardians walk a thin line, for even a single kill could leave them helplessly addicted to murder. When detective-turned-P.I. Carolyn Mathers was left at the altar, she never once thought her fiancé had been turned into a vampire. Two years later, Gray reappears, bringing murder, mystery, and an unbelievable tale of Guardians, blood-thirsty Killers, and his own transformation with him. And he's been accused of murder. A first-rate P.I., Carolyn is determined to help. Gray won't allow what he is now to taint her -- but Carolyn vows to never let him go again. But will helping Gray mean becoming a creature of the night?