In a society ravaged by centuries of war between humans and vampires, a legendary warrior priest (Paul Bettany), a veteran of the last conflict, lives in an enclosed city ruled by the church. When a murderous pack of vampires kidnaps his niece (Lily Collins), the priest breaks his sacred vows and sets out to rescue her before the bloodsuckers put the bite on her. Joining him on his quest are his niece's boyfriend (Cam Gigandet) and a former priestess (Maggie Q) with supernatural fighting skills.
For the patrons and staff at a dusty roadside diner, the day begins as usual, but when the phones go out and a sweet old lady goes on the attack, it's a harbinger of the terror to come. As the horrifying nature of the situation sinks in, help arrives in the form of the archangel Michael (Paul Bettany), who tells a pregnant waitress that her unborn baby is humanity's last hope, and he will do anything to protect it.