I thought I'd read all of Nevil Shute books, but I somehow missed this one:
Alan Duncan had flown in the R.A.F., and returns to his ancestral home on an Australian sheep ranch, wounded and disillusioned by his experiences. There he must confront a mystery: why Jessie Proctor, a housekeeper on the station, took her life days before his return. He finds her diaries, reads them, and gradually discovers her secret sadness.
My favorite of his books are A Town Like Alice and Trustee of the Toolroom.