Potentially an interesting read as I've read a few history books about the period and Elizabeth Woodville and her family, but it's a book of two halves. Firstly she's a dewey eyed woman who finds she's met the love of her life when she petitions Edward IV for her dead husband's inheritance, but later on she's totally ruthless and ambitious in her machinations to hang onto the throne for her eldest son. Even her own daughter (the future mother of Henry VIII) finds her unpleasant. 
 In the copy I have, Gregory gives an interview at the back where she says the decision to make Elizabeth, her mother, and eldest daughter all real life witches who can actually make things occur with supernatural means, such as whistling up storms, was the most fun and exciting element of the story when she was writing it. However, these are real historical characters and I think she does the story a disservice by going down that route. Far better to explore the impact on them of being accused by others of witchcraft while being without it - if she wanted that fantasy element, she would've been far better off doing an out and out fantasy alternative history or something of the sort. 
 As far as story development goes it is rather uneven. Years are skipped over or covered in very short sections of a couple of pages. Also although she starts off having Elizabeth know of remote events only through letters etc, when it comes to major battles she then does an omniscient author view which is meant to be the 'witches' being able to experience these events remotely. I'm afraid it jars although the battle descriptions themselves are OK. It would have been far better to have adopted a different character viewpoint for such scenes. 
 One thing I did like is that she followed the line that Richard III was innocent - his enemies such as the Duke of Buckingham, who had the keys to the tower, killed the princes while he was out of London, without his knowledge. (I'm not treating this as a spoiler as it is well known historically that they died, and he was supposed to have arranged it.) 
 The style is quite pedestrian and I was getting bored long before the end, I'm afraid. This is very lightweight stuff and a shame if people approach the period through this rather than novels such as The Sunne in Splendour by Sharon Kay Penman.