It's summer, 1943, and after a tough couple of years, DI Tom Tyler is making a fresh start in Ludlow, Shropshire. On the outskirts of town, St. Anne's Convalescent Hospital, staffed by nursing sisters who are Anglican nuns, has been established in an old manor house to help victims of the war to recover. After a horrifying double murder is discovered on the grounds, Tyler must figure out how the crime could have occurred in such a secluded and presumably impenetrable place.