One Step Too Far by Lisa Gardner (Author)

Timothy O’Day knew the woods. Yet when he disappeared on the first night of a bachelor party camping trip, he didn’t leave a trace. What he did leave behind were two heartbroken parents, a crew of guilt-ridden groomsmen, and a pile of clues that don’t add up.
 
Frankie Elkin doesn’t know the woods, but she knows how to find people. So when she reads that Timothy’s father is organizing one last search, she heads to the mountains of Wyoming to join the rescue team. But as they head into the wild, it becomes clear that someone out there is willing to do anything to stop them. Soon, they’re running out of time and up against the worst man and nature have to offer, discovering the evil that awaits those who go one step too far…