Truly Devious (4 book series) - By Maureen Johnson

Amateur sleuth Stevie Bell needs a good murder. After catching a killer at her high school, she’s back at home for a normal (that means boring) summer.

But then she gets a message from the owner of Sunny Pines, formerly known as Camp Wonder Falls—the site of the notorious unsolved case, the Box in the Woods Murders. Back in 1978, four camp counselors were killed in the woods outside of the town of Barlow Corners, their bodies left in a gruesome display. The new owner offers Stevie an invitation: Come to the camp and help him work on a true crime podcast about the case.

Stevie agrees, as long as she can bring along her friends from Ellingham Academy. Nothing sounds better than a summer spent together, investigating old murders.

But something evil still lurks in Barlow Corners. When Stevie opens the lid on this long-dormant case, she gets much more than she bargained for. The Box in the Woods will make room for more victims. This time, Stevie may not make it out alive.