The breaking wave / Nevil Shute.

Enhanced descriptions from Syndetics:

The Breaking Wave is one of Nevil Shute's most poignant and psychologically suspenseful novels, set in the years just after World War II.

Sidelined by a wartime injury, fighter pilot Alan Duncan reluctantly returns to his parents' remote sheep station in Australia to take the place of his brother Bill, who died a hero in the war. But his homecoming is marred by the suicide of his parents' parlormaid, of whom they were very fond. Alan soon realizes that the dead young woman is not the person she pretended to be. Upon discovering that she had served in the Royal Navy and participated along with his brother in the secret build-up to the Normandy invasion, Alan sets out to piece together the tragic events and the lonely burden of guilt that unravelled one woman's life. In the process of finding the answer to the mystery, he realizes how much he had in common with this woman he never knew and how "a war can go on killing people long after it's all over."