A royal summons is a matter of gravest importance, and Thomas Pitt, commander of the Special Branch, quickly responds when the queen calls upon him. The body of her confidant Sir John Halberd was found in the shallows of the Serpentine River in Hyde Park, killed by a blow to the head. At Victoria's request, Sir John had been investigating Alan Kendrick, a horse-racing enthusiast who holds undue influence over the Prince of Wales. As Pitt and his wife Charlotte navigate the corridors of power with utmost discretion in this 32nd entry in Anne Perry's historical series, set in the 62nd year of Victoria's reign, they uncover a threat that could topple the monarchy.