In Sydney, Australia, a Russian scientist named Nekhorvich (portrayed by Rade Serbedzija) is on a mission to develop the ultimate cure named Bellerophon for his devastating super-virus known as Chimera. His plan is to offer the Chimera virus to the U.S. Government, exposing the criminal activities of his employers. In a desperate move, Nekhorvich injects a sample of Chimera into his arm, giving himself a mere 20 hours to live before Bellerophon becomes ineffective.
Recognizing the urgency, he contacts his old friend Ethan Hunt (played by Tom Cruise), entreating him to escort him to Atlanta. However, during the flight, Ethan reveals his true identity as Ambrose (played by Dougray Scott), a rogue agent, and kills Nekhorvich before leaping from the plane, which subsequently crashes into the Rocky Mountains. Ambrose manages to steal Bellerophon from Nekhorvich’s briefcase in the process.
Ambrose’s partners, Wallis (William Mapother) and Ulrich (Dominic Purcell), assist him in his devious plans. Meanwhile, back in the mountains, Ethan, who was on vacation, is informed by his superior Michael about Ambrose's betrayal and rogue operations. Ethan learns he must form a team, which must include Nyah Nordoff-Hall (played by Thandiwe Newton), Ambrose’s ex-girlfriend.
Ethan's first encounter with Nyah reveals her to be a master diamond thief who is caught in the act of picking a secure lock for a necklace. Despite Ethan's warning about the alarm, Nyah dismisses him, leading to their capture by guards. Quick-thinking Ethan feigns that he is a security engineer, presenting Nyah as his associate testing alarms. After saving her when she attempts to escape, Nyah and Ethan share a passionate moment, and she finally agrees to join his efforts.
Later, Ethan meets mission commander Swanbeck (played by Anthony Hopkins), who discloses that Nekhorvich had left a video message for Ethan while he was away, but now it’s too late—Nekhorvich is dead. Swanbeck explains that Ambrose was once in love with Nyah and is likely to use her as leverage, making her a critical asset in locating Ambrose.
Ethan, determined to protect Nyah at all costs, injects her with a transponder chip to track her whereabouts. He orchestrates her arrest, knowing Ambrose will attempt a rescue. Upon her capture, Nyah finds herself at Ambrose's mercy, where his partner Hugh Stamp (Richard Roxburgh) is skeptical of her story, leading to a brutal confrontation where Ambrose punishes him.
In a tense game of cat and mouse, Ethan, accompanied by Luther (Ving Rhames) and Australian pilot Billy Baird (John Polson), begins to piece together Ambrose's plan, which appears increasingly sinister. He learns about the mythological reference behind Bellerophon and Chimera, relating to the creation of a monstrous virus and its potential as a weapon.
As the clock ticks down, Ethan battles against time to recover the Chimera virus before it causes catastrophic damage. In a high-stakes heist at a racetrack, Nyah cleverly steals a memory card containing information about Chimera, but Ambrose quickly realizes her betrayal.
To confuse Ambrose, Ethan enacts a daring plan that involves disguise and deception, leading to intense confrontations that test Ethan's resolve. The stakes escalate when Ambrose injects Nyah with Chimera, giving her only 20 hours to live. Does Ethan have what it takes to outsmart his nemesis and save the woman he’s come to care for?
As the climax unfolds in a thrilling showdown, Ethan faces off against Ambrose in the ultimate battle to secure Bellerophon and rescue Nyah, proving yet again that when duty calls, Ethan Hunt will stop at nothing to protect those he loves.
