Alison Weir's account, Mary, Queen of Scots and the Murder of Lord Darnley (Cape, £20), hinges on the assassination of Mary's second husband, Lord Darnley; Jane Dunn's book, Elizabeth and Mary: Cousins, Rivals, Queens (Harper-Collins, £20), on Mary's relationship with her cousin, Elizabeth I. Weir's effort shows her usual strengths and weaknesses. It is, as ever, a highly readable tour of familiar ground.