Crimson Shore by Douglas Preston and Lincoln Child
I've been reading Preston and Child books for a long time, and I still think Agent Pendergast is among the most intriguing protagonists ever. If you haven't read any of the Pendergast books, I recommend them. They are all good. These are mystery-thrillers, but they all have some element of macabre or sci-fi, which is why they appeal to me so much (the first of the series is Relic, which should give you an idea of what I mean). In Crimson Shore, Pendergast decides to take some "time off" to investigate a basic case involving theft of a valuable wine collection. As you can guess, this case turns into much more than that—grisly murders and a town with dark secrets.