I'm a little torn on this one. Barnard is a great writer and you can see the Agatha Christie influence on this one: the manor house, the village "types," the sympathetic detective, and, unfortunately, the playing fast-and-loose with time. I enjoyed the book although it creeps into the red zone on the Irony Meter.
Sarah becomes governess to a charming child of the engaging local upper-class Hallam family in a classic Tudor mansion, leaving her dysfunctional family behind. It seems too good to be true, and it all starts to break down when the body of a young man (as well as a fake skeleton) is found on the grounds.
Barnard tries to confuse us by moving back and forth in time, so that all we know is that Sarah has not only survived, but thrived. However, she is one of the few. The murder, though, takes place during the early months of the Spanish Civil War (ca. 1936) and the denouement during the Blitz, in 1941, barely 5 years later. In fact, the perpetrator confessed in 1939. This is hardly "old history" for a murder case and I doubt any police detective would just say, "Oh, you've suffered enough and it was really only an accident." That's for a court to decide.
Agatha Christie would have written something fiendish that tracked down a murder committed even in the distant past! But she also strained credulity - notably in her play "The Mousetrap." The murderer is too old to have been the student of one of the other characters who is too young - unless the teacher retired after teaching one year and the murderer was 18. I've seen two - thirty year olds playing these respective parts. Well, heck! No wonder no one can guess the ending (unless they've seen Stoppard's send-up: "The Real Inspector Hound").
[Side note: I've performed in both of these shows, always as a character 20-30 years older than I was at the time, so I'm not quibbling about the age of actors.]