Detective Erin O'Reilly is no stranger to close calls. She and her K-9 Rolf have dodged more than their share of blades, blasts, and bullets as they've taken on the worst New York City has to offer. But the last perp came a little too close, leaving one of Erin's fellow officers with a bullet-hole in his head and her own brain scrambled.

Erin needs a break, but as her long-running infiltration of the O'Malley gang enters its final act, she can't afford to slack off. And that's not her only headache. When a former convict turned pizza deliveryman has his skull crushed in a college parking garage, an apparent mugging may be something much more sinister. Banging her head against one problem after another, Erin faces obstacles both on the street and in herself. She'll have to break through to the answers before her own brain lets her down.