A Place to Bury Strangers (Beatrix Rose Book 4) by Mark Dawson

Under a slate-grey sky on the desolate expanse of Salisbury Plain, an early morning dog walk takes a chilling turn. When Jan Lewandowski's spaniel, Coco, abandons her tennis ball to race past a warning red flag into a restricted military zone, she unearths something far more sinister than a toy. Amidst the churned-up tank tracks and memories of military warnings, a long white bone is brought to light. What begins as a routine stroll threatens to uncover dark secrets buried within the restricted training grounds.