Hercule Poirot is approached by Mrs Todd with a case. She wants Poirot to investigate the disappearance of her cook, Eliza Dunn. To Poirot it looks like nothing more than a domestic leaving her employer but he reluctantly takes the case. He and Captain Hastings set out to the Todd household in Clapham, where nothing significant turns up. Through advertisements in newspapers they track down Eliza Dunn. The story behind her departure piques Poirot's interest and he starts to think that something far more sinister may be afoot.
The first episode of the wonderful Poirot series, and it's a good one. Quite short by comparison with most of the later episodes but it crams a lot in. Intriguing, especially as the story develops from searching for a domestic who likely just changed employers to something much more interesting, and illegal.
As a bonus, we have the entire gang present - Poirot, Japp, Hastings and Lemon - and the more of them there are in an episode, generally the better it is.