Series 2 is the first to have a series-long "B-story" beginning with the first episode and ending with the series finale.
Sidney's typewriter is a 1951-9 Remington Quiet-Riter.
Both Tom Austen (Guy) and Morven Christie (Amanda) made guest appearances in Poirot. Austen had a minor role, while Christie's was more substantial.
Al Weaver and James Norton also star together in Life in Squares.
Al Weaver plays another character named Leonard in Life in Squares.