It's by the author of Rebecca-- and like Rebecca, its plot hinges on an enigmatic woman whom we "know" (if know we can) through the eyes of others. Like Rebecca, too, it raises issues regarding the character of her spouse... And there's murder involved, possibly two murders. Maybe. It depends.
However, if by the end of Rebecca I knew exactly how to judge each character, My Cousin Rachel-- a complex, gripping, suspenseful narrative-- left me bewildered, shaken, mildly obsessed. My mind went over and over it for days... Is Rachel-- formerly the Contessa Sangalletti-- evil, manipulative, and murderous; or merely manipulative; or innocent of all conscious design? What to think of the two men (in many ways, the same man) who married her? Is their narration trustworthy, and to what degree are they complicit in their own destruction? Are they better or worse than she is? Are they guilty? And what of cultural difference? ...Unlike Rebecca, My Cousin Rachel offers no "correct" perspective, but leaves us to draw our own conclusions.
If we can. I'm still uncertain of mine!