While the original novel already had its sad moments, there are quite a few in this adaptation that are wholly its own.
- We get a new origin story for Poirot. He was an ordinary corporal serving in the Belgian army in World War I. His company was ordered on a risky attack that might've wiped them out, but Poirot, observing the birds, told his captain that if they attacked right then, the wind would work perfectly to cover their attack with smoke gas. He was right, and the company took the near side of the bridge with minimal casualties. But then, at the last minute, his captain accidentally triggered a Booby Trap, killing him, and maiming Poirot. So that despite his brain helping to save most of his men, he instead is haunted by the life he couldn't save and the scars that would forever remind him.
- Despite putting on an act, Jacqueline's monologue about her love for Simon feels quite heartbreaking in the heat of the moment.
- Poirot reminiscing about his first love during the war. That he asked her to come out to see him for the holidays, and she ended up killed during a bombing raid. Showing another guilt that he's had to hide during his life.
- Before turning in for her last sleep, Linnet tells Jacqueline that she is sorry that the business with Simon came between them. And that despite everything, she did appreciate that Jacqueline was the only person to whom friendship came without regards for her money. Even for just a moment, it seems like Jacqueline has a moment of guilt before putting her plan into action.
- The sad fact that Linnet was utterly wrong... it was all about Linnet's money for Jackie.
- Dr. Windlesham angrily, and sadly telling Poirot that he knew that Linnet only planned to "settle" for him, but despite it being for image, he had fallen for Linnet before she broke it off.
- Poirot having to guiltily reveal to Rosalie, Salome, and Bouc that he'd been hired to do a background investigation by Bouc's mother into their relationship to find something bad about Bouc's hopeful intended. He doesn't, but this doesn't make anyone happy.
- Poirot realizing that his last interview HAS to be with his informal assistant, because he realized that Bouc was hiding a secret. Anger, sadness, and disappointment that his old friend could betray his trust by lying about so much....and then he's shot.
- Poirot is angry at Bouc during the interview, but it drops instantly when Bouc is shot. Poirot is so shocked and horrified that he reverts entirely to his native French: "Bouc! Mon ami...!"
- Then he charges, unarmed after the shooter, even engaging them in close combat before the assailant escapes. Before, it was just a case. Now, it's very very personal.
- Looking over Bouc's corpse, Rosalie mentions to Poirot that Bouc always partially hoped that Poirot would find happiness and not worry about being so smart. But now that he's dead, Rosalie gives a sad remark that, "I don't want you happy. I want you to find out who did this."
- Poirot for his part briefly is choked up with grief when recounting what Bouc had seen in his parlor speech.
- Then on realizing the truth, Rosalie in angry grief swears that Jacqueline will die for this.
- Linnet Doyle's last words.Linnet: [smiling] Simon...
- The fact that everything that happened occurred because Simon was greedy and Jackie was driven so mad by her desire not to lose him. Five people died and many other lives were utterly ruined because Simon couldn't live honestly and Jackie couldn't see that Simon was no good for her.
- Has Bouc's mother just accepted that he loved Rosalie then Bouc would have lived. Her own bitterness over her love life cost her the last person that loved her.
- Dr. Windlesham woefully telling Poirot on disembarking, "There's nothing for me in England." Linnet was his last connection to his old life, so he sadly makes plans to do good elsewhere in the world.
- Salome with a bit of disappointment, telling Poirot that "I almost wish I didn't get to see you work." The very thing that allowed him to find justice turned out to be the same thing that pushed her away from Poirot.
