The second episode of Series Four was an adaptation of Death in the Clouds, first published in 1935. The novel was adapted for television by William Humble and directed by Stephen Whittaker.
Script versus novel
Humble reworks, transforms, edits and omits several passages from the novel. In fact, apart from the basic plot, most of the surrounding material is changed. I'll try to go through the changes one by one. First, Humble adds a series of scenes before the actual plane journey, set in Paris. These include a scene where Jane Grey and Poirot meet outside the Sacre Coeur, a scene at the hotel in which Poirot overhears a conversation between Lady Horbury and her maid, an entire tennis tournament (with Fred Perry, who was referred to in previous episodes like The Veiled Lady and Peril at End House) at Roland Garros attended by all the suspects and Poirot, several scenes that embellish the back stories of Lady Horbury, Venetia Kerr and Lord Horbury (who is present in Paris in the adaptation), a scene in which Poirot and Jane Grey visit a modern art gallery, and a scene in which Poirot observes Lady Horbury and Madame Giselle. These added scenes make complete sense, and some of them are referred to (but not outlined in detail) in the novel. The tennis match (in keeping with the producer's wish to include real-life events) is a nice substitute for the novel's casinoes in Le Pinet.
Second, several characters are omitted, including Mr. Dupont sr. (Jean Dupont, his son, briefly explains that his father died some years before and that he is planning a new archaeological expedition), Mr. Ryder, Dr. Bryant and Giselle's concierge George. The three passengers are hardly missed, since Jean Dupont takes on some of his father's characteristics; Poirot, Norman Gale and the police take over the doctor's role; and Mr. Ryder is essentially just a red herring in the novel. The concierge character is so minor that his lines are easily linked to the maid/companion Elise instead. (MORE AFTER THE JUMP)
Third, several of the remaining characters are somewhat changed. Jane Grey, who works as a hairdresser in London in the novel, becomes one of the two stewards (replacing the youngest steward) - a very sensible change, since it enables her to have a more active role in Poirot's later investigations. Also, Poirot does not attempt to match her with Jean Dupont as he does in the novel. Inspector Fournier, whose role is significantly reduced by the increased presence of Japp (who travels to Paris to investigate with Poirot), is portrayed as a somewhat more annoying police inspector than in the novel (at least in Japp's eyes), providing some gentle comic relief. Lord Horbury has a greater presence in the adaptation, too. He is present in Paris and consults Poirot in London to explain that his wife isn't a murderer. His affair with Venetia Kerr (hinted at in the novel) is somewhat more obvious here. Also, Daniel Clancy is more eccentric in the adaptation, as he has conversations with his detective (sort of reminiscent of Ariadne Oliver in later episodes). Generally speaking, these character changes do not distract from the storyline. In fact, they seem to enhance it in some of these instances.
Fourth, several passages are completely or partially deleted. Most importantly, the interviews with the various suspects are shortened down, and quite a lot of the discussion between the three investigators on the case (Poirot, Japp and Fournier), as well as Poirot's lists and reflections, are reduced. Chapters that are cut out include 'The Inquest', 'After the Inquest', 'Consultation' (but some of Madame Giselle's background is explained by Lady Horbury to Poirot), 'Probabilities' (Poirot's overview - but he checks them with the experiments on the plane), 'The List' (but the most important luggage, that of Norman Gale, is shown on screen as Japp examines it), 'The Little Black Book' (in fact, the entire issue of who could have been Giselle's "victims"), 'The American' (only parts of it are kept), 'At Antoine's' (not needed since Jane has become a stewardess), 'Plan of Campaign', 'At Muswell', 'In Queen Victoria Street' (the character has been deleted), 'Enter and Exit Mr. Robinson (Gale instead disguises as a journalist in Paris on Poirot's request), 'In Harley Street' (the character has been deleted), 'The Three Clues' and 'Jane Takes A New Job'. In sum, though, the deleted scenes aren't really that missed, unless you know the story by heart. I'm sure the main reason they were deleted was time constraints.
Apart from the changes and additions outlined above, the adaptation stays fairly close to the original novel, keeping large sections of dialogue in the process. Subjectively speaking, I don't think it's a bad adaptation. In fact, I think it proves the point that a word-by-word adaptation isn't always the only acceptable solution - despite being significantly reworked, the adaptation still retains much of the spirit of its source material, and its changes make sense.
Directing, production design, locations, soundtrack
Stephen Withttaker makes great use of the Paris locations. The opening sequence wonderfully sets the tone, with Poirot walking up the stairs to Sacre Ceur, and there are some lovely shots of the plane crossing the Channel. My only objection, perhaps, is that we get a few too many shots of the Eiffel Tower. I mean, we get the point, you are filming in Paris. There's no need to show us the landmark every other minute. (But that's a minor quibble, really). The production design is outstanding, and the recreation of 1930s aviation is impressive. The locations used for the episode include Palais de Tokyo, 13 Avenue President Wilson (the modern art gallery), Theatre des Champes-Elysees, 15 Avenue Montaigne (the hotel), Palais de la Porte Doree, 293 Avenue Dausmesnill (the town hall), Le Bourget Airport (the central 1930s section of the building), Shoreham Airport (Croydon Airport), "La Palette" cafe, 43 Rue de Seine (the meeting between Poirot and Lady Horbury). Cimetiere de Passy (the police station). Gunning's soundtrack was released on his first Poirot CD, but it is not included on the re-release. Thankfully, it's on YouTube.
Actors and characters
There's a lot of Poirot characteristics in this one. Notice, for instance, the collection of walking sticks and leather suitcases that he brings with him on the plane (they will all be seen in later episodes, even up to the most recent ones - an impressive sense of continuity in his wardrobe). Then, of course, there's his airsickness (delightful comedy acting from Suchet), his initial interest in Daniel Clancy's detective fiction (which will culminate in his magnum opus in Third Girl) and his gentle behaviour when talking to women in distress or out of touch with the setting they're in (like Jane Grey). Also, Japp gets some delightful scenes as he becomes a fish out of water in Paris (Christie never brought Japp abroad, but he goes abroad twice in the series, to Paris and Brussels (The Chocolate Box) - and possibly again for the upcoming adaptation of The Big Four.
Of the guest actors, all manage to flesh out their characters in various ways. Of course, the two 'deputy investigators' Sarah Woodward (Jane Grey) and Shaun Scott (Norman Gale) do a nice job, but I'm actually quite intrigued by Cathryn Harrison (Lady Horbury), who gets to develop from an initial borderline stereotype to a somewhat more likable and fully fleshed character during the course of the investigation.