Darker Than Night — John Lutz

A killer dubbed "The Night Prowler" has turned the city that doesn't sleep into a town kept awake by terror. Unseen, he enters couples' homes. Unsuspected, he lingers until the perfect moment arrives. He leaves "gifts" for his victims--before taking their lives.

Enter ex-homicide cop Frank Quinn, still reeling in the wake of an elaborate setup that ended his career. For Quinn, this isn't just any job--it's a last chance to salvage his reputation. As the investigation proceeds, the murderer loses no time stalking new prey: a loan officer and her high-earning husband; a couple who made a killing in the stock market; a pretty actress and her prosperous lover.

With the body count rising, it's up to Quinn to unlock the mystery of a madman's past and end his bloody reign. Quinn's got his work cut out--because in a city the size of New York, any one of 8 million faces could be that of a killer--or his next target...