Unquiet Grave — P.J. Parrish

Not Every Soul Rest in Peace
In a remote corner of the Michigan woods, behind rusted iron gates and crumbling stone walls, lie one of the country's most notorious sanitariums and its forgotten cemetery. The sprawling ruin is empty now, and the bulldozers have come to raze it. But as they do, a terrifying secret begins to emerge.

The body in Claudia Olsen's grave is that of a stranger who died horribly. This much Louis Kincaid knows. But what happened to the woman who should be buried there? It's a question no one will answer, one that leads Kincaid to the long, dark tunnels below the asylum and crimes of unimaginable depravity...

Now, in a place where the walls are stained with secrets, the air thick with the lingering history of screams, Louis Kincaid is on his darkest journey yet, matching wits with a monster whose work will not be silenced...