When Timothy Harris came on the scene with Kyd for Hire in 1978, I thought of him as a direct descendant of Raymond Chandler and likely to become a top writer in the field. It never happened, even though his second novel, Good Night and Good-Bye (a direct bow to Chandler) was even better. Instead of following up on that one, Harris got into writing movies, and I'm sure he made a lot more money from them than he'd have made from writing p.i. novels.
In 2004, Harris came back with a third Thomas Kyd book, Unfaithful Servant, published by Five Star. Nothing more, though, that I'm aware of. If you like p.i. novels, you can't go wrong with any one of the three, but you'll want to start with Kyd for Hire. That's the paperback cover over on the left. The British hardcover came first, I believe, but it's probably way too expensive.
There's a good interview with Harris on January Magazine.