(Note: Semi-spoiler for the the ITV Double Sin adaptation.)
In the ITV Agatha Christie’s Poirot adaptation of the Poirot novella The Incredible Theft, Poirot investigates the titular crime while staying at the home of his politician-client, while sidekick Captain Arthur Hastings and Scotland Yard ally Chief Inspector Japp (who are not in the original) have to make due at a pub so crowded they have to share not only a room but a bed.
Now, in both the books and the series, Hastings’ and Japp’s relationship is open to interpretation, and not in the “slashy” way – quite the opposite. They appear to have their differences at times. I sense some competitiveness over who is “the” sidekick and best friend to Hercule Poirot.
But in The Incredible Theft, Hastings’ principal complaint about Japp as a roommate is the noise he makes. First a bang and a crash as he takes off his boots. Then (so Hastings reports to Poirot), “[Japp] talks in his sleep: ‘Now I’ve got you, young-feller-me-lad! Japp-of-the-Yard strikes again!’….Stand back lads, he’s got a [here Hastings uses a word that sounds like “bla-maj” (I’m using phonetics – the word “blamage” actually means “disgrace.”)
This may seem like pure comic relief, but with a poke just slightly beneath the surface, something is revealed about Japp as a character.
He dreams of deeds of investigative derring-do, – in other words, he longs to be, and be seen as, a Great Detective. But a Great Detective who speaks French? Could that mean he wants to be just like Poirot?
(In fact, in the Double Sin adaptation, Japp reveals in a speech just how much he respects Poirot.)