Captain Hastings makes a passing remark to Miss Lemon about wanting to travel to South America and try farming. In the book version of this story, he meets the woman whom he later marries. They would move to Argentina and he becomes a farmer.
Poirot meets Countess Rossakoff again in The Big Four, but her character is omitted from the episode adaptation. He meets her for the final time in The Labours of Hercules (2013), this time portrayed by Orla Brady.
Poirot here uses his knowledge of correlations between the Russian and Latin alphabets to assign ownership of a cigarette case found at the scene of the crime. Agatha Christie also had the Poirot character use this knowledge to assign ownership of a monogrammed handkerchief to Princess Dragomiroff in Murder on the Orient Express.