Dark Stars by Megan Derr

In the sleepy town of Briden, nothing ever happens—not unless you know where to look. Bobby Thurston is one of the few capable of doing that, and so is often enlisted by local problem solver Harold Legrasse to keep the dangerous things that creep at the edges of the known world from causing too much harm.
Then he’s hired to solve a mystery that bears strong resemblance to the kind of trouble once caused by Bobby’s grandfather. Trouble that begins with cultists and nearly always ends with far too many people dead. Unlike his relatives, Bobby has no desire to see humanity wiped out… but when it comes to crazy cultists bent on murder, he has no qualms about playing with his food…
But he’s not the only one on the hunt, and the stubborn hunter he comes across refuses to stay out of the way as bid. More intriguing still, the peculiar, obstinate Alejandro has a soul untainted by corruption, unheard of in blood-soaked hunters who are generally happy to kill without ever bothering to ask questions.