The Vein by Steph Nelson

It’s 1989 and failed detective, Syl Dixon, has returned to her childhood home in Pate, Idaho, to sell the old place she grew up in, back before her grandma mysteriously disappeared. But when the shriveled corpse of a local man is discovered inside the old silver mine the town was built around, Syl is unexpectedly asked to help investigate. She's reluctant, but something about the town has unnerved her from the start, and she can't help but feel that her grandma's disappearance is connected somehow. Once on the case, she learns that the mystery behind the man's death goes deeper than the old mine where his corpse was found, and involves an evil that has plagued the town for nearly a century.