Night Secrets by Thomas H. Cook

Frank Clemons, an ex-cop turned private detective, faces a pair of perplexing cases on the mean streets of New York City

The first case is simple. A wealthy man's wife has grown distant, and he asks Frank Clemons, a private eye hardened by his past work on Atlanta's homicide beat, to find out why. There are a number of simple reasons why a young woman might withdraw from her older husband, but the spurned spouse rejects them all. Her jewelry is disappearing, but he insists that she doesn't have trouble with blackmail, drugs, or gambling. The answer must be more complex, and he begs Frank to find out what it is.

Meanwhile, an old woman familiar to Frank from his nights haunting Tenth Avenue has been murdered, and a gypsy priestess claims that she killed her. But Frank is unconvinced, and unearthing these women's secrets will force him deep into the dark side of a city that he still cannot call home.

Night Secrets is the third book in the Frank Clemons Mysteries, but you may enjoy reading the series in any order.