Her life was also a bit complex; her first husband fell in love with somebody else and declared his intention to marry his lover. During the course of this controversy, she suddenly vanished, could not be found, sparking a nation wide frenzy. She was found 10 days later, with the room booked in the name of her husband's lover; at her being found, there was relief but there was also criticism that she was either trying to setup her husband or doing a marketing stunt.
Sad Cypress is one of those books where there is a spectacular twist in the end, with almost no clues during the course of the book (revealing anything about the twist would be like a spoiler, so I shall desist from that, but will detail a bit of the plot of the book).
It is the age old story; a couple in love, Elinor and Roddy, engaged to be married, not very rich but the rich aunt looking on lovingly on the couple and happy with their decision. And then the boy comes into contact with another girl, one who stays with the aunt and he falls for her (and about whom the couple is warned about, that she is threatening to steal the affections of the aunt and inherit the money). The engagement gets broken off, and in the meantime the health of the aunt declines. She asks that money be settled onto this orphan girl, Mary. Soon after the aunt dies, leaving her fortune to Elinor, while Roddy gets nothing.
And then suddenly, when Elinor is clearing the house after the death of her aunt, Mary dies of morphine poisoning and the most obvious person is suspected and on trial. Poirot is engaged, and the rest of the book is about his sleuthing to find who actually committed the murder and whether the person arrested by the police were indeed guilty. Most of Poirot's books don't really show court proceedings (in some cases, the coroner investigation is shown), but in this book, the case is shown in court.
For Agatha Christie fans, a book certainly worth reading; if you haven't read Christie before, then a good book to start with.