The Stone Circle — Elly Griffiths

In a chilling entry to the award-winning Ruth Galloway series, she and DCI Nelson are haunted by a ghost from their past, just as their future lands on shaky ground.

DCI Nelson has been receiving threatening letters. They are anonymous, yet reminiscent of ones he has received in the past, from the person who drew him into a case that's haunted him for years. At the same time, Ruth receives a letter purporting to be from that very same person -- her former mentor, and the reason she first started working with Nelson. But the author of those letters is dead. Or is he?

The past is reaching out for Ruth and Nelson, and its grip is deadly.