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...