I love Daphne du Maurier, and bought this book recently. It was one I hadn't heard of.
It took me a bit of time to get into it, but when I did I really enjoyed it. But the end really puzzled me.
I gather from what I've read that DdM also left it open/deliberately vague.
I'd be really interested if anyone else has read it, to know what your theory is about the ending? It's left me feeling vaguely dissatisfied!