The year is 1969 and ten guests are about to enjoy a weekend at Tavistock Hall. The guests also include 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. The house's owner – a penniless, dope-smoking aristocrat – is intent on selling the estate to a secretive millionaire but the weekend has only just started when the millionaire goes missing and murder is on the cards…