In the breathtaking Italian Alps, an MI6 team embarks on a perilous mission to extract a potentially dangerous asset and arms dealer, Mulvaney. Tasked with this challenge is Rachel Stone, who, despite being officially part of the tech support crew alongside Bailey, must infiltrate a ski lodge casino to hack into security systems. With internet connectivity down, she is left with no choice but to physically access the phone of the head of security to obtain the crucial encryption key.
In her attempt to maintain her cover, Rachel engages in a single hand of blackjack, only to seem to vanish shortly thereafter. Meanwhile, field agents Parker and Yang gain entry to the restricted area of the casino, uncovering that some patrons are wagering on the body count of an ongoing combat situation involving US Navy SEALs and terrorists. They soon realize that someone has breached military-grade encryption.
Their original plan to induce a fake heart attack in Mulvaney fails as his bodyguard intervenes. Nevertheless, Parker manages to isolate Mulvaney, leading him onto a cable car. Their communication lines, however, are compromised by Keya Dhawan, who reveals that she was aware of the MI6's arrival.
Seeing more of Mulvaney's security team converging at the cable car station, it becomes evident that Parker's survival hinges on the urgency of the MI6's arrival. As a ruse, Rachel pretends to sustain a twisted ankle, allowing the MI6 team to proceed without her. Subsequently, she contacts Charter, a covert peacekeeping organization, in hopes of assisting the MI6 agents incognito. Through Jack of Hearts, she receives guidance to position herself ahead of the cable car and is equipped with a parachute to ski down the mountain.
In a display of courage, Rachel neutralizes the six-man security detail, concealing their bodies. Unfortunately, Mulvaney manages to ingest cyanide before they can capture him. Back in London, the MI6 team faces reprimand for the mission's failure. Later, as they unwind, discussions arise regarding the enigmatic Charter, believed to consist of elite ex-intelligence agents operating outside governmental confines. MI6 suspects that Keya may be associated with Charter and is alarmed by the compromised military encryption.
Rachel journeys to Charter's headquarters, where Nomad chastises her for her reckless tactics. Charter has successfully tracked down Keya, a young hacker whose extraordinary capabilities were nurtured by a billionaire and who later fell in with criminals. Now 22, Keya orchestrated the casino ploy to lure Mulvaney, who was in pursuit of a powerful Quantum Computer known as "The Heart," which possesses the ability to hack into any system globally.
With Keya's whereabouts pinpointed to Lisbon, MI6 sets a plan in motion to ambush her. However, while Rachel is offered an escape route by Jack, she chooses to stay and aid her teammates, inadvertently exposing her identity. In a tragic turn, Parker eliminates the rest of her team and reveals he has a hidden agenda concerning "The Heart." He discloses that it is the source of Charter’s strength, possessing the capacity to predict future occurrences. Ultimately, only a Charter member can identify its location.
In a cruel twist, Parker injects Rachel with a hacking device. After she is retrieved by Charter's recovery team, Keya utilizes the device to infiltrate their systems and access The Heart. Reacting swiftly, Rachel manages to stab herself to remove the device, but not before the impending systems breach. Jack impressively determines that The Heart is stationed in a blimp called The Locker, soaring at 85,000 feet, and advocates shutting it down immediately due to the uncertainties regarding Keya’s intentions.
Nomad then relegates Rachel from the mission, blaming her for their failure, stating that had she escaped as instructed, lives would have been spared and The Heart secured. Charter assigns titles to its agents, akin to a deck of cards, and Nomad along with the other Kings convene to discuss Parker's motives. They reveal his harrowing past in Chechnya and how Charter had orchestrated a drone strike that he barely survived, leaving him with a thirst for vengeance.
Determined, Rachel uses Keya's hacks to locate her again, tracking her movements to West Africa where she is intent on commandeering The Locker. Keya's hack threatens to destabilize The Locker's altitude, leaving Parker with a brief window to seize The Heart. As Charter's forces find themselves too far from the blimp, Rachel skydives from a plane to reach the airborne facility.
Onboard The Locker, a fierce showdown ensues as Rachel confronts Parker, while Keya makes a move to snatch The Heart. As Parker makes his escape, Rachel grapples with Keya, leading them both into a freefall until they deploy a parachute, safely landing in the Senegal desert. Despite Parker now possessing The Heart, it remains ineffective in his hands, as it requires Keya’s biometric access.
Rachel’s compassion prevents her from eliminating Keya, as she knows that Keya's intentions stem from a tragic past tied to a billionaire whose experiments claimed her parents. Instead, Rachel proposes that Charter can dismantle Niam’s influence without obliterating Keya’s aspirations. A tracker is discreetly placed on Keya as they reach a town, only to face an ambush by mercenaries hired by Parker.
Just as Rachel narrowly escapes, Keya becomes a captive. Fortunately, she finds solace with another Charter agent, Six of Hearts, who assists her rescue. This leads them to Iceland, where Rachel briefs Nomad and strategizes an operations strike against Parker to prevent him from activating The Heart.
As Rachel traverses Iceland, Parker capitalizes on The Heart's capabilities to execute malicious attacks, including on members of Charter. Even as Keya struggles with the violent outcomes, Rachel maneuvers through obstacles, with Keya ultimately aiding her against Parker. After a climactic battle, Rachel successfully shoots Parker down and Keya manages to deactivate The Heart, allowing the Hearts team to breathe easy. In the aftermath, Rachel offers Keya an opportunity to join the Charter, marking a new beginning for both.
