I'm sure about a couple of things. One is that MacDougall had studied Ross MacDonald and Lew Archer. If you don't like the Archer series, you're not likely to enjoy this book, which seems to me to be quite reminiscent of Macdonald's work. It has the same seriousness of purpose, the same kind of tangled family problems. And speaking of seriousness, the other thing I'm sure of is that MacDougall took his work seriously. He probes deeply and gets into his characters like few others in the p.i. game.
The story's a common one. A young girl is kidnapped. Her family is distraught. A p.i. (David Stuart) is brought into the case by an old friend. The kidnapping is resolved, but there's a lot more going on, and Stuart is in the fine tradition of investigators who take things personally, who can't quit if loose ends are dangling. Before it's over, as often happens, he wishes that he had quit, but he hangs on until the bitter end. And bitter it is.
MacDougall's well worth re-discovery, and if you'd like to give him a try, both his novels are easily (and cheaply) available.