This is not really one of the classics. It's watchable, as are all the Poirot episodes, but the actual crime itself and the final explanation is a little bit far fetched.
Not quite sure why a production that is about to transfer to Broadway supposedly would have its first outing at a humble English seaside resort, nor why the presence of a highly expensive necklace is so necessary to what is an incredibly creaky play. Given that, the story does rattle along. The necklace, which is always kept inside a locked box inside a drawer is stolen, despite the presence of the maid in the room at the time of the supposed theft. How could it happen?
Needless to say it takes Poirot's little grey cells to finally work it all out, but the clues are there for the viewer (some of them a bit obvious too). The denouement takes a few liberties, but it's good, clean fun, as they say.