Fans of the London Weekend Television Poirot series may be surprised by this adaptation of the first of the novels. While ingredients familiar from the rest of the series are here, the feel is rather different, probably because the story is set in 1917. The Art Deco backgrounds that are a hallmark of the rest of the series are missing. We are treated instead to the dark, cluttered luxury of an English country estate, improbably well appointed for war time, as a familiar cast of suspects move in and out of the ample shadows.
The episode is a little unusual in the central role played by Hastings, and even more unusual in its concentration on character. Most of the LWT Poirot adaptations focus on the puzzle, garnish it with playful character touches, lush backgrounds, and superb cinematography. This segment, probably because it is establishing the relationship between Poirot, Hastings and Japp (in a relatively modest role), spends more time on the interaction between people. As a result, the pace of the segment is also slower than most, perhaps also in an attempt to convey the feel of a vanished way of life.
The episode is a particularly beautiful example from a series that specialized in gorgeous period evocations, with ample response to lush green landscapes, the creeping darkness of an early summer evening, or the harsh light slipping through the blinds of a shuttered room. The Moderne look of the thirties episodes here gives way to a slightly seedy Edwardianism, obviously past its prime, but still holding on to remembered glories. (One of the nicest touches is that the victim, an elderly matriarch, dresses in a manner more appropriate to some fifteen years earlier.) Even the graphic design of the credits has been changed, substituting a more traditional serif font for the curvilinear, Plaza type used in the other episodes.
In short, if you can imagine one of the better English "Heritage Films" of the past few years crossed with the forward movement of a Christie detective story, you have a good sense of what to expect from "The Mysterious Affair at Styles." Somewhat atypical for the series, it is also one of the most subtly atmospheric episodes.