Hall of mirrors - Christopher Fowler

The year is 1969 and ten guests are about to enjoy a country house weekend at Tavistock Hall. But one amongst them is harbouring thoughts of murder. . .
The guests also include the young detectives Arthur Bryant and John May - undercover, in disguise and tasked with protecting Monty Hatton-Jones, a whistle-blower turning Queen's evidence in a massive bribery trial. Luckily, they've got a decent chap on the inside who can help them - the one-armed Brigadier, Nigel 'Fruity' Metcalf.
The scene is set for what could be the perfect country house murder mystery, except that this particular get-together is nothing like a Golden Age classic. For the good times are, it seems, coming to an end. The house's owner - a penniless, dope-smoking aristocrat - is intent on selling the estate (complete with its own hippy encampment) to a secretive millionaire but the weekend has only just started when the millionaire goes missing and murder is on the cards. But army manoeuvres have closed the only access road and without a forensic examiner, Bryant and May can't solve the case. It's when a falling gargoyle fells another guest that the two incognito detectives decide to place their future reputations on the line. And in the process discover that in Swinging Britain nothing is quite what it seems
So gentle reader, you are cordially invited to a weekend in the country. Expect murder, madness and mayhem in the mansion!