I love this book, and I came across this excellent review in The Guardian:

Wilkie Collins's The Woman in White is the ultimate page-turner. I must have read it four or five times, and the strangest thing about it is that every time it induces the same hunger in me to get to the end and unravel its mystery. I've often wondered why it is that on each rereading I seem to have forgotten much of its byzantine detective plot of illegitimacy and switched identities, and am ready to be drawn afresh into its labyrinth. I suspect that it's partly because the novel forces you, even against your will, to read it at a single sitting with such speed that many of the narrative details go no further than your short-term memory.

But though it is one of the earliest and best mystery stories in the canon, The Woman in White isn't just about plot. What does stick even after a single reading, and gets enhanced and modified with each successive exposure, is its use of image, character, narrative voice and theme. The arresting scene in which a woman dressed all in white appears out of the darkness on a lonely road is unforgettable - even more so when one knows its origins in Collins's own biography. One night, as he walked a friend home, he himself had encountered such a figure, "a beautiful young woman dressed in flowing white robes that shone in the moonlight", who had approached in "an attitude of supplication and terror".
In real life, Collins took up this enigmatic woman of questionable background, Caroline Graves, and made her his mistress, living with her in a parody of "respectable" domesticity, yet concealing her existence from all but intimates. In The Woman in White, Collins seems like a conduit for the Victorians' troubled attempts to define womanhood - in terms of class and respectability, looks and sexual appeal, strength and weakness. The two heroines , Laura, blonde, vulnerable and childlike, and Marian, feisty, intelligent and ugly, enact one split in Collins's blocked attempts to define a good woman. Laura and her lower-class lookalike Anne Catherick provide another play around the ideas of identity and difference.

Indeed, shifting identity is The Woman in White's central theme. Written as it is from the viewpoints of different characters, it is a novel without a centre, and the tension between this and the linear pull of the mystery narrative is what gives it such uncanny power.
Lucasta Miller, The Guardian

RELEASE NOTES:

I just nipped into HAC to release my copy of "The Picture of Dorian Gray" which I've recently finished reading, and found this book on the shelf. It's one I started to read years ago but sort of drifted away from before finishing it - I'll try to do better this time!