I always really enjoy reading Weir's books but I've never been impressed by her as a historian, principally because of her very biased and uncritical use of sources. I've found it best to treat her as a historical novelist putting forward an almost fictionalised version of the story she is telling. In this book, she has attempted something a little different from the other books of hers I have read: to untangle a mystery, rather than elucidate a personality as she does in her books on Eleanor of Aquitaine and Isabella of France. And, sadly, this just serves to foreground and highlight her weaknesses.
While this purports to focus on the murder of Darnley, it's almost impossible to untangle that event from so much else in Mary's life, and so the book also treats their marriage, her possible affair with Bothwell, the murder of Rizzio etc etc. My main criticism is that in her discussion of the sources at the start Weir states she is basing her interpretation on Nau's `official' account, as if this is somehow unbiased and objective reporting. But she also admits that Nau's account probably came to him from Mary when he was acting as her secretary - not so unbiased after all then. How this is more objective than what she calls the `hostile' sources isn't tackled at all.
My second, broader criticism is that Weir appears to believe in her unproblematic ability to uncover, for once and for all, the `truth' of Darnley's murder. In her thought world there appears to be no room for possibilities, probabilities, no nuances and no alternatives - despite the fact people have been arguing over this question ever since it happened over 400 years ago.
And yet despite all this, Weir's Mary is not significantly different from the other Marys who have come down to us through history. As usual, she is irrational, emotional, hysterical - and it never occurs to Weir that this is the standard description and understanding of women in this period (Elizabeth, too, is frequently described in the same terms) based on Galenic physiology which makes women subject to the humours of the womb. Similarly she picks up on a mention of Darnley being `effeminate' and takes a C20th interpretation, postulating that he might have had homosexual tendencies. Later, the same term is used about him again but in relation to his having returned to sharing Mary's bed where it clearly means that he is under a woman's rule, but she doesn't use this to shade her previous interpretation in any way.
Overall this is quite a clumsy book and it doesn't have the same readability of some of her others. For a good popular read on Mary I would still recommend Antonia Fraser's
Mary Queen Of Scots which may be old now, but is still far superior both historically and literarily to this.