In Farleigh Field by Rhys Bowen

In this World War II thriller, a parachutist falls to his death in a field outside Farleigh, the stately home of Lord Westerham and his daughters. The dead man's uniform leads people to believe he is a German spy, sent to contact a traitor at Farleigh or in the nearby village. Lord Westerham's middle daughter, a codebreaker at Bletchley Park, works with an MI5 agent who is a family friend to discover who the traitor could be.