Hercule Poirot returns to Brussels after 20 years, traveling along with Inspector Japp who is invited there to be honored for his services to Belgium. Meeting his assistant from the days when he was still just a rookie police officer, Poirot remembers an old case from that period - the death of an ambitious Belgian government official that was attributed to heart failure. Poirot claims that the verdict was wrong, and proceeds to tell Japp the whole story.
"The Chocolate Box" is one of the best "Poirot" episodes since "Wasp's Nest", mainly for the same reason: because it moves away from the usual formula of the series and tries something different. It offers a glimpse at the earliest parts of Poirot's career - earlier even than "The Mysterious Affair At Styles" where he had already moved to England. It's also one of the very rare instances where we see Poirot involved in a subtly romantic relationship with a lady (the lovely Anna Chancellor). There is no investigation in the present - Poirot had actually solved the case in the past, and we get to see how in some beautifully done flashbacks. And the case is really quite simple - the clues are right there in front of you, but you still won't notice them. (***)