At this point, one side plot of the movie is solved. We can see Major Barry arresting Horace Blatt. As a matter of fact, Major Barry was an inspector from Scotland yard. He was hiding for a month to investigate the drug dealing that was going on, on the island. That explains also why he could not say anything and was so cold and serious: he was afraid that Poirot might ruin his cover and had to keep his mission secret. We can even see an action scene, which is actually too violent for the genre in fact: in the book there are no action scenes.
One side mystery is now solved and exonerates a few characters from having committed the murder. Horace Blatt was a drug trafficker, he was importing heroin over sea, and the bird watchers were getting in back in the country. They used the cave on Pixie Cove because no one remembered its existence. He used the colour of his sails to indicate if the area was safe or not to bring the drugs.
Now comes the answer. Japp, as usual, gets the wrong end of the stick when it comes to drawing parallel between this murder and Alice’s. He concludes that in both cases, the husband must’ve been the culprit, and therefore thinks Marshall is the man. But Poirot has a different opinion and is going to make it all clear. As usually in detective stories from the early 19th century, the detective gathers all (remaining) characters in one room, in this case: the dining room. He then gives a speech, as if talking to a classroom, in which he unveils the solution to the murder. He proceeds by elimination, accusing rather violently each of them, and playing with their respective feelings of guilt one by one before exonerating them. He starts explaining that he has seen Arlena differently from all others there. As Most saw evil in her, Pirot saw Arlena around her. With other words, from the moment he met her, he saw her as an eternal and predestined victim and not as a wicked woman. He explains that by the fact that Arlena had a fatal weakness for men who took advantage of her, rather than men having a weakness for her.
He first accuses Kenneth, saying his alibi is not worth anything because he has not been seen, explaining that having been married to Arlena must have been a torture. Someone else could have been typing instead of him while he was commiting the murder. Lionel’s spectacles found on the crime scene and the fact that Lionel was alone for a short time was also a lead against Lionel. The only statement about the time provided by him and Christine, was Lionel’s watch, he could have lied about the time, or changed it on his watch. Christine would not have been able to verify it.
Miss Darnley had a good motive: Arlena stood between her and Kenneth. Emily Brewster also had a motive: Arlena ruined her play, made her loose a great deal of money. Miss Redfern among all had a good reason to get rid of her, as Arlena was stealing her husband. Even reverend Lane, who stood up saying he couldn’t do it didn’t know what to answer when Poirot said he would have wished to see her punished, like his Jesabel of a wife.
Christine reminds Poirot of the blackmail lead then, which he quickly casts aside. The letter they found, taken like a threat, was to be considered in his opinion as a fact: you’ll lose a great deal, if you don’t invest more money into this. The phone call Christine overheard a phone call, but she only knew what was said on one side.
Now Poirot emphasises how he thought no one could have committed the murder *alone*. And then explains how the real evens unfolded.