Marnie: by Winston Graham.

One feels a surprising anxiety for the poor unfortunate girl caught between her past - which one presumes cannot have been choice as much as concatenation of circumstances not of her choice, which she dealt with by stealing and so forth as a strategy for survival. Now, she is not only married to a wealthy man who loves her, but she loves him and would rather not lose him - and he is finding out about her. the only other source of strength for her is the horse, and she could die in an accident