Death At Windsor Castle (1998)
(The third book in the Her Majesty Investigates series)
A novel by C C Benison

Housemaid Jane Bee's summer duties run to dusting the props for a week of pageantry at Windsor Castle, the Queen's favorite haunt. But the Investiture of the new Knights of the Garter ends up combining pomp with a extremely unpleasant circumstance. Mild-mannered art curator Roger Pettibon is found dead, a ceremonial sword in his back and a Royal Garter around his knee.

The police are quick to arrest moody Court painter Victor Fabiani, at work on a portrait of the regal face that launched a billion postage stamps. But Fabiani's confession despite its story of art forgery and blackmail doesn't ring true to Jane. Nor to Her Majesty, who dispatches her on a discreet inquiry among the cream of society gathered for the Ascot races. And, as Jane traces the twisty lineage of more than one family, Windsor's ancient battlements witness a second death and their second ordeal in five years, by fire and water...