Script versus novel
Gatiss makes quite a number of changes to the source material without making them feel too 'added' (and that - as we will see in Appointment With Death - is not always an easy task!). His job is not an easy one, particularly because this is one of Christie's more incredible plots (like The Big Four and The Clocks, this story brings Poirot into contact with the world of espionage and secret agents!). The most important (and I'm tempted to say the most essential) change he makes is to add Poirot to the proceedings much earlier than in the novel (where it takes almost two-thirds of the story before his name is even mentioned). Instead of having Julia Upjohn introduce him, he arrives with the other students at the beginning of term, and we are told that he is an old friend of Miss Bulstrode's (a very sensible change). In fact, he is there as a guest of honour to present a Pemberton Lacrosse Shield award. Later, he is persuaded to stay on and help Miss Bulstrode find the right successor to the school (again, a sensible change). I love his cover story, posing as a representative for King Leopold of Belgium (of whom he is a friend in the Christie novels). Moreover, Gatiss deletes several of Christie's characters, including Col. Pikeaway, Mr. Robinson (a very wise decision), Briggs the gardener, Denis (Ann's boyfriend, whose role is partly given to Adam), Henry Sutcliffe - and Eleanor Vansittart (the third candidate for new headmistress). The latter character's characteristics and fate are partly inherited by Miss Rich. He also adds two students to the proceedings; Patricia Forbes (presumably added to showcase Miss Springer's temperament) and Hsui Tai (who gets to discover an effigy of Miss Springer, which is also added to the plot). Further changes include making Shaista Ali Yusuf's fiancé, changing the murder weapon used to kill Miss Springer from a gun to a javelin (a much more satisfying, almost horror-film inspired death), deleting Mlle. Blanche's identity theft (but keeping her blackmailing scheme) and the question of the ownership of the jewels. The script also changes the nature of a significant witness in Ramat from peeping-tom neighbour to one-time lover, (needlessly). Furthermore, the death of Rawlinson and his associate is changed from an airplane accident to a brave shoot-out in Ramat, and the robbery/search of the Upjohn's hotel room is removed (but referenced in the dialogue). Finally, some sections from the novel are removed, including the letters from the students to their parents, the mysterious American woman / the culprit in disguise, and the end scenes, and some scenes are added, including Poirot observing the teachers at the school, Poirot pretending to lose a map on the floor to look at Shaista's knees, Miss Bulstrode's visit to Ann's insane mother (rather than a countess), and a new end scene with Poirot, Julia and her mother. All in all, Gatiss's adaptation succeeds in streamlining a very untraditional Christie story and making the changes feel both natural and necessary.
Directing, production design, locations, soundtrack
James Kent's direction is wonderful to watch. I particularly like the many transitions between scenes. For instance, in the well-directed opening sequence, the tennis rackets in the sports pavilion are compared to the guns of the rioters in Ramat, and the boy in the car, playing with his toy gun is compared to the shoot-out scene in Ramat. Also, the scenes in which Poirot observes the teachers are well done, and so are the different murder scenes. The direction goes well with Stephen McKeon's music, locations and production design, all contributing to the (dear I say it) Harry Potter / boarding school atmosphere. The main location used is the Sue Ryder Home in Nettlebed, Oxfordshire (previously seen in the adaptation of Sad Cypress), doubling as Meadowbank School.
Characters and actors
It's always nice to see Poirot reacquainted with old friends (even if the friend wasn't a friend in the novel). Also, I like the small touch of Poirot's phone call to George (keeping his presence in Poirot's life - much like his calls to Miss Lemon in earlier episodes). Also, the mention of his meeting at the Foreign Office to return the rubies almost feels like a homage to the short story (and adaptation) 'The Theft of the Royal Ruby'. Of the guest actors, Harriet Walter (Miss Bulstrode) is the main standout, perfectly balancing the strict headmistress aspect and the humanity of the character, but most of the actors feel perfect for their roles and do a great job.