I've read several of Du Maurier's books and this is one of the weaker ones. It's a classical psychological thriller and asks the question "did she do it?" in the earliest pages. The narrator never answers the question, but provides enough clues for the reader to make up their own minds. The writing is crisp and descriptive, I just couldn't get into the characters. "Did she do it?" I don't think so, but the next reader may decide she did. 
 Edit: 
 I featured this book as part of an article published in the bookcrossing newsletter. Here's the excerpt regarding this book: 
 "From Florence we wandered the countryside. Like the 19C English tourists in My Cousin Rachel we visited hilltop towns that had changed little from the Middle Ages, watched stunning sunsets over the Tuscan hills, tasted the local wine, and ate the local delicacies. We even took a side trip to Ravenna--a favorite destination for those on the "Grand Tour" (and mentioned in the book I'm currently reading Brideshead Revisited. There, we admired the 5C mosaics at the Mausoleum of Galla Placidia (the protagonist in my second book), biked the cobblestone streets (a jarring experience!), and ate divine gelato." 
 The entire article is here.