"The Devil's Queen: A Novel of Catherine de Medici" paperback by Jeanne Kalogridis.

From Publishers Weekly: In this soap opera rendition of 16th-century power and politics, the ruthless and manipulative wife of France's King Henry II, reviled for her role in the civil and religious wars that roiled France, is conned into a deal with the devil. After her arranged marriage to the future French king, Catherine de Medici dedicates her life to protecting her husband and his reign, bartering away her soul to ensure that she provides heirs. Seasoned historic novelist Kalogridis (The Borgia Bride) nails the palace intrigue and lush pageantry of the Renaissance, but can't get a grip on her heroine's slippery, troubled heart. Catherine confesses to a core of evil, and history certainly supports that view, but Kalogridis suggests that the real trade-off of Catherine's Faustian bargain was to become a royal doormat, swallowing her courage and pride to become a dutiful and ignored wife and mother. For all her passion and attention to detail, however, Kalogridis doesn't quite bring the powerful, tortured figure back from her historical purgatory.

From School Library Journal: Catherine de Medici (1519–89) was the wife of one French king and mother to three. Intensely disliked by the French and kept in the background during her husband's reign, she came into her own after the death of her eldest son. The period of her strongest influence was also one of great political and religious unrest in France; she will be forever associated with the St. Bartholomew's Day massacre of French Protestants. Making her hardcover debut with this well-researched and highly readable historical novel, Kalogridis (The Borgia Bride) treats Catherine with far more sympathy than most chronicles. In this portrayal, Catherine is highly superstitious, and her dealings with the astrologer Ruggieri lead her to commit unspeakable acts for the sake of her husband and children. In the end, though, fate cannot be cheated, and Catherine must deal with the consequences of her actions. Good for most collections, especially those where historicals are in demand. There are a couple of graphic sexual scenes, but they are not gratuitous.