Murder on the serpentine

the long version

"It is not the custom for the commander of Special Branch to receive a royal summons-- so Thomas Pitt knows it must be for a matter of the gravest importance. The body of Sir John Halberd, the Queen's confidant, has been found in the shallow water of the Serpentine in Hyde Park, bearing the evidence of a fatal blow to the head. At Her Majesty's request, Sir John had been surreptitiously investigating Alan Kendrick, a horse-racing enthusiast who seems to have had an undue amount of influence on her son, the Prince of Wales. Now Commander Pitt must navigate the corridors of power with the utmost discretion and stealth, for it seems certain that Sir John's killer is a member of the upper classes. Aided by his wife, Charlotte, and her social contacts, Pitt seeks out the hidden motives behind the polite façade of those to the manner born-- and uncovers a threat to the throne that could topple the monarchy."--Amazon.com