This is the premise of Whitley Strieber's Alien Hunter novel. It's basically a cop thriller with an extraterrestrial angle thrown in. That alien aspect of the story is the most valuable part of it for me simply because it reflects Whitley's experiences with apparent alien contact that he has documented in his nonfiction books and on his website. So his depiction of the aliens and how they operate has the feel of UFO anecdotes--mysterious lights, frightening entities glimpsed in the dark, and time-condensed abductions. This adds a "reality" to the alien scenes that make them interesting above the usual such in science fiction stories, but they become more "typical" when he gets down his characters' actual interaction with the aliens. That is, the aliens become less alien and more human in their criminality.
The storyline, despite the alien angle, is pretty much typical for the cop thriller genre--a hard-boiled detective goes searching for the abductor of his wife, finds a sexy partner along the way, handles guns, flies planes, talks tough, and fights it out with the bad guy in the end. Now if you're just really into this genre, and a lot of people are, then you may very well like this book, especially if you're open to the science fiction angle. But it failed for me just because I didn't find the lead character interesting. I didn't find any of the characters interesting, actually, though Mr. Strieber did throw a slight twist at the end concerning the sexy partner that kind of broke the mold.
My best takeaways from this book were the parts of the alien scenes that I detected as being from real UFO stories and from Mr. Strieber's experiences. Also the aliens' use of genetically engineered animals was an interesting component that could have been enlarged. And more, in the midst of the usual thriller plot, Mr. Strieber adds an observation that should have been a major theme but that lost much from not being supported by interesting action and sympathetic characters. This is the feeling of isolation in someone with knowledge of bizarre and appalling situations that are not suspected by the people around him. This is expressed in Alien Hunter in Flynn Carroll's thoughts as he considered the people around him in a store:
He understood the origin of Diana's inner distance. It was having secret knowledge of a larger world that did it. They were innocent, he was not.
I considered this the story's highpoint, and the rest of it didn't measure up.