Not a Drill by Lee Child (2014) Transworld Digital

Jack Reacher, hitchhiking up to Maine, catches a ride with a group of hippies who want to hike a specific trail in the woods.  When they get to the hiking trail the hippies want to go on, they’re barred by the army, who won’t let anyone on the trail.  One of the hippies, who doesn’t like to hike, left, going to the other end of the trail to pick them up at the end.  But the hippies disappear.  Reacher is intrigued, even more so when the driver returns, expecting them to be there.  The trail is next to a lake, so they rent two kayaks and go half-way down the length of the trail, crash in and start to back track, hoping to run into the hippies.  Instead, they find a dead body.