The War Above The Fence. A Claire Harmon Mystery, #8

For the first time, Claire Harmon doesn't have to go looking for trouble - it moves in two doors down from her own front porch. When a routine boundary survey turns up a small discrepancy along the fence line dividing her quiet cul-de-sac, it looks like nothing more than an inconvenience between neighbors. Then a beloved widower turns up dead in his own garden, and the disputed strip of ground becomes the edge of something far older, and far worse, than a property line.
On a street of casseroles, coffee on porches, and neighbors who have known each other for decades, someone has been keeping the most careful secret imaginable - and keeping it well. As Claire pulls at a truth buried twenty feet from her own back door, she has to answer a question none of her previous cases ever asked of her: can the ordinary life she has built survive discovering that evil doesn't always arrive from somewhere far away? Sometimes it waters its own garden, waves every morning, and lives right next door.
For fans of Liane Moriarty, Lisa Jewell, and Ruth Ware.