There's something uglier than usual on the streets of San Diego-Tijuana. It's big and mean. Some say unkillable.

Specialist Calley Reid isn't so sure. Dormac, her wardog, agrees. They've never met anything they haven't been able to stop.

A chance encounter with a victim nearly killed by one of these creatures puts them on the trail of something unbelievable. Which leads her to the mystery surrounding their incredible origins, and the lunatic plans of the fanatics using them.

What's coming could tear everything apart, unless Calley, Dormac, and the unit they work for can find a way to stop an invasion like nothing ever seen before.