The Sleeping Partner by Winston Graham
'When someone isn't home when you expect them to be, and when after a decent interval they still don't turn up, and send no message and have left no note, it's natural to get anxious. But there's still a lack of decisive event. Your ears are all the time waiting for the click of the door, the quick familiar footsteps, and the breathless apology. So I didn't do anything more to find her that night.' Why has Lynn Granville left her husband Michael? Because he is never at home? Because at work Michael has an extrememly attractive new assistant whose marriage has its own problems? Or because she herself has created a new life that does not involve him. And why are the police taking such a criminal view on what surely must be a domestic case?