Falling Immortality by Robert Downs

Private detective Casey Holden has just gotten back from a vacation of fun in the sun when he gets an unexpected visitor, Felicity Farren. Her husband was killed two years ago, and the local cops have let the case run cold. She wants answers, as well as justice, and Casey appears to be the right man for the job. Since he’s intrigued by Felicity, and since he doesn’t have anyone else knocking on his door, Casey takes her case. But when he starts digging for the truth, he soon realizes this isn’t a simple crime, and he probably doesn’t have a big enough shovel...