Script versus novel
Horowitz remains largely faithful to the novel, but there are several minor changes. First, he had to reintroduce the Big Three properly, just as he had started doing with Lord Edgware Dies. The solution this time around is to add an Argentinean restaurant, in which Hastings has invested much of his capital. Japp and Poirot attend the opening night (Miss Lemon, of course, is 'way behind with her filing'). This scene allows the three leads to be acquainted with Arlena Stuart, Kenneth Marshall and the man who is later believed to have been blackmailing Stuart. It also provides a rather humorous reason for Poirot to go on holiday - he is admitted to hospital and is considered 'medically obese' (later revealed to be food poisoning, and Hastings's restaurant is obviously to blame - another bad investment). In turn, the Jolly Roger Hotel becomes Sandy Cove Hotel, a health resort, and all the guests are admitted with (more or less plausible) health issues. Also, throughout the episode, Poirot complains of the diet programme he has to follow (on Miss Lemon's orders, of course). This subplot / introduction is actually quite nicely handled, and it does make Hastings's (who is not in the novel) presence feel somewhat more plausible. Second, several insignificant guests are deleted, including Mr. and Mrs. Gardener, the Cowans and the Mastermans.
Third, Linda Marshall, Kenneth Marshall's daughter, becomes Lionel Marshall here. He is revising for his chemistry exams and borrows a book at the library on poisons (rather than Linda's weird obsession with witchcraft). Also, making the child a man provides a handy extra suspect (Lionel's glasses are found misplaced at the scene of the murder - not a pair of scissors, like in the novel).
Fourth, Rosamund Darnley - who speaks of a friend of hers who was in Egypt when Poirot was there - is here an old acquaintance of Poirot's from that very same holiday. She is still an old friend of Marshall's, though, and Horowitz even adds a scene in which Poirot overhears a conversation between the two that is potentially incriminating for her. Fifth, Chief Inspector Japp replaces Inspector Colgate and Colonel Weston, the Chief Constable (the latter was replaced by Japp in Peril at End House, too, so that makes sense, I guess). Sixth, Major Barry's hunt for the smuggler's ring is linked with the visit of two bird watchers (a couple who want to dine at the restaurant in the novel). Seventh, Lionel doesn't try to commit suicide, like Linda does in the novel. Eight, Miss Brewster is given a motive for murder - she lost a significant amount of money by investing in a play Arlena Stuart pulled out of. Ninth, Miss Lemon gets to investigate in London and Blackridge (first, looking into the details of Stuart's will, second, looking into the previous murder that Stephen Lane is linked to). Tenth, the potential blackmail is explained (quite cleverly) by the differences between British English and American English - "lose a great deal".
All in all, though, almost all Horowitz's changes are sensible and are primarily made to add extra twists and turns. It's not a great episode, but there is not much wrong with it either.
Directing, production design, locations, soundtrack
Farnham's direction is competent and somewhat straight-forward. He makes excellent use of the great location (Burgh Island hotel - the very hotel at which Agatha wrote the novel!). Other locations include Salcombe, South Devon (the very same location that was used for Peril at End House, which, judging by several references in the novel, took place not far from the hotel), and the Blackridge scenes were shot in Buckinghamshire - Hambleden Church and Frieth Village Hall. Gunning's soundtrack is well executed. It has not been released.
Characters and actors
It's nice to see the development of the main character relationships (even if, by now, it does seem to strain credibility a little, if you ask me). I particularly enjoy Pauline Moran's display of utter shock when her employer is admitted to hospital - she is obviously concerned and wants him to be all right, a display of the affection she has for him. Her concern for his health equally so. Of the guest actors, there doesn't really seem to be any standouts in this one. They all do a competent job, but that's that. A young Rusell Tovey can be spotted playing Lionel.