Just as this was the golden age of detective fiction, it was likewise the golden era of ‘classic sleuthing’, characterised by ‘handwritten notes, disguised identities, and long vigils from parked motorcars outside suspicious properties’.

Here we again enjoy the almost absurd success of various elaborate disguises: an imposter posing as the Prime Minister; a woman doubling as her own maid; a man living a double life as businessman and petty thief, his own wife seemingly unaware of the false beard he is sporting.