A seductive street-level peek at the world of Gil Lewis, real-life Boston private eye: ""I'm a shadow, an invisible man drifting through other people's lives."" A nondescript guy who drives a nondescript car and can blend into any crowd, Lewis has been in the business 20 years and is one of the best--he tracked down Howard Hughes in six hours, by phone, for the National Enquirer. But most of his work falls into more mundane categories: ""domestic"" jobs, missing persons, and criminal defense investigation. His is a night world--""Everything's in black and white, like a forties movie. I like it""--and a solitary one. In ""domestic"" cases (i.e., getting the goods on straying spouses), his specialty is surveillance: the establishment of ""inclination and opportunity""--which for Lewis often means long nocturnal vigils slumped in the front seat of his car. (He doesn't moralize, though: ""I know my client is probably doing just as much as the spouse I'm following."") Who becomes a missing person? Surprisingly, more middle-aged women than anyone else. Lewis sports a near-perfect batting average in finding the missing (through techniques as exotic as staking out a mother's grave at holidays), though he confesses that disappearances often defy logic: how do you explain ""the guy who leaves his wife because she's too religious, only to run off to Sarasota with a nun?"" He refuses to get sidetracked by mysteries (""people are really very simple--they do things for reasons""), except in criminal defense work, where his job is to put pieces together. Lots of short case histories here: finding the people responsible for harassing and threatening gay politician Elaine Noble; tracking down defense witnesses for a police officer accused of murder; posing as a sheet-clad guru to find a young runaway in Cambridge; talking a transsexual hooker into testifying in court in a murder case. Through it all, Lewis tries to stay uninvolved: ""Only the facts are any use . . . if I thought too much about what I see, I'd jump off the Prudential Tower."" Sedgwick first covered Lewis' exploits for a Boston newspaper, and his low-key narrative fits the investigator's understated style. A very entertaining slice of life.