Script versus short story
Horowitz remains more or less faithful to the short story, with several important additions and changes. First, the reason for Poirot's and Hastings's stay at the hotel is that Poirot needs rest (one of his overworked/hypochondria/retirement moods). Second, he adds an unnecessary running joke concerning 'Lucky Len', a character from a newspaper, which looks remarkably like Poirot. Third, the Opalsen couple are using the pearls for a play, called 'Pearls Before Swine', and they are very concerned about publicity (both getting it and keeping it). This gives the adaptation a set of new characters, like Andrew Hall, who has written the play and knows Celestine well (a suspect for the theft eventually) and Hubert Devine, an actor, who explains that the Opalsens are keen to succeed with the plat due to money trouble. Fourth, Celestine, the maid, isn't French (instead, there's a reference to her mother being French), and Saunders is a chauffeur and not a butler to Mr. and Mrs. Opalsen. Fifth, Japp - who is mentioned in the story - is added as the investigating officer. So is Miss Lemon, who gets to question different people in London (she finds out that the pearls would have been too famous to be sold in the UK and would have to be smuggled to the US). Sixth, there's a separate clue added, in the shape of the mysterious Mr. Worthing (who later turns out to be one of the culprits in disguise) - and Poirot partly solves the case through a reference to 'The Importance of Being Earnest' (where the character is called Worthing - much like Arden in Taken at the Flood and Murder on the Orient Express). All in all, though, the adaptation seems to work, and the changes are - for the most part - understandable.
Directing, production design, locations, soundtrack
Grieve's direction is competent. I particularly enjoy his use of cameras inside the drawer and the vase at the theatre. The production design is faultless as usual. Locations used include Butlins Ocean Hotel, Saltdean (now converted into luxury flats), the Eastbourne Pier and the Devonshire Park Theatre, Eastbourne. Gunning's soundtrack is memorable and well executed. It has not been released.
Characters and actors
Of the guest actors, Sorcha Cusack* (Mrs Opalsen) and Hermione Norris (Celestine) stand out.
*The Cusack family is an interesting one in the Poirot universe. Sorcha appeared in this episode, Niamh Cusack in 'King of Clubs' and Sinead Cusack in Dead Man's Folly. That's quite extraordinary!