Comedic Sociopathy: Japp is notably amused when he finds out Poirot is in jail for being caught as a burglar. Given that they're friends, though, he still gets Poirot out after getting some things cleared up.
Detective Patsy: Lampshaded by Poirot, who points out that even the criminals of England try to get him on their side when they need his skills.
Evil-Detecting Dog: Just when the search for the two suspects is growing cold, Hastings hears a meow from a random cat, who sneaks in to their hiding place and rubs on them, all the while meowing and purring. It doesn't take long for Hastings, Japp and Poirot to figure out where the suspects are.
Foreshadowing: A news report seen in a paper early on talks about a man found murdered in the Netherlands. Said man happens to be the actual Laverton, and the one Poirot meets turns out to be an impostor.
It Will Never Catch On: A character who lives in Wimbledon comments, "It hasn't been the same 'round here since they started the tennis up the road. You get all these riff-raff come to watch!"
Mundane Solution: Captain Hastings heroically runs after a blackmailer to try to find out where he lives. Poirot doesn't bother joining Hastings. He looks the blackmailer's address up in the phone book.
Nobody Here but Us Statues: The two suspects hide in a museum exhibit and pretend to be mannequins under the sheets among other mannequins while Poirot and his team are on the search for them until their search is growing cold. The mannequin statue plan almost works... until a Cute Kitten comes along and discovers the suspects, all the while meowing and purring.
Screw This, I'm Outta Here: Hastings bails out of the burglary operation when he and Poirot realize that the police might be on to them. Fortunately, he's the one who gets to handle the crucial item they went in for - and to alert Friend on the Force Japp of Poirot's predicament.
Super Window Jump: When both Poirot and Hastings are cornered by the police for burglary, Poirot distracts them, allowing Hastings more time to run toward the windowed back door exit with the special Chinese fortune box in his hands. But by then the door is locked, so Hastings gets a moment of awesome by jumping out through the window, smashing the glass from inside.
Surprisingly Realistic Outcome: Poirot, being older and less spry than Hastings, gets caught during their burglary operation while his friend made a successful escape.
Whole-Plot Reference: This episode, as well as its source material, both call back to the Sherlock Holmes story The Adventure of Charles Augustus Milverton, where the eponymous detective and Watson break into a blackmailer's house to retrieve a crucial item. Of course, Agatha Christie put her own spin on the story.
