As Hercule Poirot steps off in Aswan, eager for a serene expedition along the Nile River on the opulent Karnak, he encounters the charming yet complex Linnet Doyle née Ridgeway, played by Gal Gadot. Linnet seeks Poirot’s aid to manage her former friend Jacqueline de Bellefort's (character A) incessant obsession. Recently wed to Simon Doyle (who was once Jacqueline's fiancé), Linnet finds herself the target of Jacqueline’s intense jealousy and animosity. Poirot, however, decides against taking the case and attempts to counsel Jacqueline, who remains steadfast in her grievances. Meanwhile, Linnet and Simon secretly track Poirot’s movements, soon realizing that Jacqueline has cunningly boarded the steamer ahead of them. The passenger list reveals an array of fascinating characters, including Linnet's devoted maid Louise Bourget; her trustee Andrew Pennington; the captivating romance author Salome Otterbourne and her daughter Rosalie (Letitia Wright); Tim Allerton and his mother; the elderly American socialite Marie Van Schuyler, her cousin Cornelia Robson, and her nurse Miss Bowers; vocal communist Mr. Ferguson; archaeologist Guido Richetti; solicitor Jim Fanthorp; and physician Dr. Bessner. The stage is set for a complex web of intrigue and motives.
Amidst sightseeing at Abu Simbel, chaos erupts when a colossal boulder barely misses crushing Linnet, leaving the passengers in shock and raising eyebrows about Jacqueline’s potential involvement, although she was present onboard at the time. As tensions rise, Colonel Race, a loyal ally to Poirot, joins the journey back on the Karnak, harboring a secret motive: to uncover a perpetrator among the guests.
That evening, following the incident, Jacqueline unleashes her wrath on Simon in the steamer's lounge, where she carelessly fires a gun, hitting him in the leg before collapsing in regrets and chaos ensues. With Fanthorp and Cornelia quickly escorting her away, Simon receives medical attention from Dr. Bessner. The search for Jacqueline’s gun yields nothing, but an even graver revelation awaits: Linnet is discovered dead, her precious string of pearls missing. A previously reported stolen velvet stole is soon found wrapped around the pistol, which was identified to have been fired recently—an unsettling reminder that peril lurks around every corner on this journey marred by deceit and murder.
As Poirot speaks with Louise in a hidden cabin where Simon is resting, he notices her unusual way of speaking, hinting at deeper secrets. Meanwhile, Miss Bowers returns Linnet's pearl necklace just to unveil it as a skillfully crafted imitation, a clever trick devised by none other than the kleptomaniac Miss Van Schuyler. Poirot's intrigue is further deepened by two nail polish bottles found amongst the belongings of the victim, one possessing particular significance. In a grim turn of events, Louise is discovered brutally murdered in her cabin, prompting Mrs. Otterbourne to meet with Poirot and Race, claiming to know the identity of the murderer, only to be silenced by a sudden barrage of gunfire from outside.
The investigation takes a swift twist when Poirot confronts Pennington regarding his earlier attempt to kill Linnet using the rogue boulder. It becomes apparent that Pennington, driven by financial motives and ambition, intended to manipulate Linnet into signing papers that would absolve him of wrongdoing while he pursued her riches. Despite his denials of further involvement, Poirot connects the dots to find that Pennington's revolver was the very weapon used to kill Mrs. Otterbourne.
Digging deeper, Poirot uncovers Linnet’s real pearls from Tim, a crafty thief who had mastered the art of swapping out the genuine article for imitations. Focusing his investigation further, Race closes in on the elusive Richetti.
Poirot shares his shocking uncovering with Bessner, Cornelia, and Race, unveiling that Simon was, in fact, responsible for pulling the trigger on Linnet. Jacqueline had orchestrated this deadly deceit, aiming to shield her lover from blame. It was revealed that Linnet's ploy to create distance between Simon and Jacqueline gave Simon the perfect opportunity to take drastic action. As chaos broke out, Simon feigned injury, staged a self-inflicted gunshot wound, and expertly manipulated the scene, laying evidence to deceive investigators.
In the chaos that followed, Poirot becomes fixated on Louise's peculiar behavior. She had witnessed Simon's clandestine entrance into Linnet's cabin and cunningly dropped hints to extort him. Determined to protect Simon from exposure, Jacqueline resorted to stabbing Louise, ensuring her silence. Tragically, Mrs. Otterbourne stumbled upon Jacqueline as she entered Louise's cabin, leading to her own swift demise, orchestrated by Simon's frantic warning.
In a tense confrontation, Simon confesses to his venomous deeds, resulting in his arrest alongside Jacqueline and Richetti. As the Karnak docks at Shellal and passengers disembark, Jacqueline seizes a final chance to escape justice, shooting Simon and herself with a second hidden pistol. When questioned, Poirot acknowledges he was aware of Jacqueline's secret firearm but had decided to grant her agency over her fate, leading to a conclusion both tragic and unavoidable.
