This is a startling work for anyone familiar with Zola. What Zola has written here is a fairy tale. It is a fairy tale set within a framework of realism and the only works that I know that are similar to it are Silas Marner and to some degree The Hunchback of Notre-Dame.
Even more surprising is the fact that the book is one of the Rougon-Macquart series, but it is utterly unlike the others. It concerns a young woman who has a dream which is essentially a fairytale of marrying a handsome prince. This fairytale is set within a context of the medieval view of Saints and Miracles. None of that is that surprising for Zola, but what is surprising is that this fairytale essentially comes true (albeit in a bittersweet way). The book seems to eschew commentary on the Second Empire and also to eschew (at least mostly) the sense that blood is destiny. It is fantastical and primal like a good fairy tale and commits to the internal logic of a fairytale.
Obviously, the Frech Fairy Tale tradition is very strong and I have always found that French fairy tales are the most satisfying psychologically, but even though the book is set within a contemporary realism, Zola is about the most startling author to write this way. I can hardly imagine a less likely author. There are hints that Zolas characteristic irony and sense of the foibles of human delusions are going to break out at anytime. Furthermore, the whole thing is wrapped around with Catholicism, that Zola barely mocks at all.
It is completely surprising for a Zola novel land its inclusion within the ROugon-Macquart sequence shows that we are meant to take it seriously. It is however, surprising and difficult to get one's head around. It's a very pretty tale and, appropriately, very dreamlike. I don't know what to make of it, and it is very much a Zola curve-ball. It is at least average in quality for Zola however, and worth reading, especially by someone who has read enough Zola to be startled by it.
Zola at his least Zola-ish.