Nevertheless, it’s hard to ignore the fact that the plot has been moved, unnecessarily, from the 1920s to the Fifties and that the once youthful hero is now a mature married man with an uncanny resemblance to the late Frankie Howerd.
More importantly, the adaptation takes its title from the second book in the series rather than the original 1922 mystery thriller, The Secret Adversary, which introduces adventure-seeking Tommy and Tuppence Beresford, Christie’s youngest detectives.
The duo, who are both adjusting to civilian life after the First World War, have barely two halfpennies to rub together and decided to advertise their services - they are willing "to do anything, go anywhere".
Inevitably, The Secret Adversary is a little dated – when did you last address someone as “old bean?” But in other respects, it mostly stands the test of time. The plot is character driven and, though nobody worries about the Bolsheviks anymore, we’re still getting our knickers in a twist over foreigners with different philosophies and young people still act first and think afterwards.
It’s an undemanding read that rattles along at a good gallop although there are some anachronistically crude stereotypes that don’t sit comfortably. Tommy, for instance, is “pleasantly ugly, yet unmistakably a gentleman” whilst a member of the criminal set has low beetling brows and a criminal jaw “and the bestiality of his whole countenance is of a type that Scotland Yard would recognise at a glance”.
Not classic Christie but, overall, a charming period set-piece. Worth every penny.