In the film, the story begins in 2003 inside a prison where Court Gentry, played by Ryan Gosling, is visited by Donald Fitzroy, portrayed by Billy Bob Thornton. Fitzroy is a CIA recruiter who reviews Gentry’s criminal background and offers him a chance to work for a classified program called the Sierra Program. Gentry accepts the offer, setting him on a path of covert operations that will span over two decades.
Fast forward to 2019 in Bangkok, and Gentry has become an elite CIA assassin operating under the codename "Sierra Six." His latest mission involves eliminating a target known as "Dining Cart," a mission that seems straightforward at first. Assisted by Dani Miranda, played by Ana De Armas, Gentry moves in to take out Dining Cart’s associates. Throughout the mission, he is monitored closely by his superiors, Denny Carmichael, depicted by Rege-Jean Page, and Suzanne Brewer, played by Jessica Henwick.
As the operation unfolds, Six chooses to deviate from the plan when a child appears at the scene, prompting him to abandon the target temporarily. This decision leads to a confrontation where he and Miranda eliminate Dining Cart’s guards and finally face Dining Cart himself. During their intense fight, Six manages to fatally wound Dining Cart, who then reveals a shocking truth—he is "Sierra Four," a former operative whom Carmichael had ordered Six to kill. Before dying, Dining Cart gives Six a necklace that contains a chip with crucial information capable of exposing corruption within the CIA.
In the aftermath, Carmichael contacts Six to deny that he recovered anything from Dining Cart, attempting to cover up the real story. Six then tries to access the sensitive data on the chip but hits a wall as he lacks the necessary login code. He contacts Fitzroy from Baku, concerned that Carmichael is a corrupt figure hiding damaging secrets about his operations.
To eliminate Six, Carmichael enlists the help of Lloyd Hansen, played by Chris Evans, a former CIA agent with a reputation for brutality. Hansen, stationed in Monaco, is shown torturing a suspect, highlighting his ruthless methods. Hansen’s determination leads him to kidnap Claire, Fitzroy’s niece, to coerce information.
Meanwhile, Six is ambushed during an extraction in Chiang Mai. Recognizing the trap, he fights off the team capturing him and causes the plane they are on to explode, showing his resourcefulness and combat skills. He then reaches out to Fitzroy, who informs him that Hansen has Claire. Flashbacks reveal Six’s earlier life in London, where he bonded with Claire—a fragile girl with a heart condition—while under Fitzroy’s protection. His connection with her becomes a focal point, motivating his actions to protect her from the mounting danger.
Following the bombing, Six travels to Vienna to meet with a contact named Laszlo Sosa, played by Wagner Moura. Initially seeking help to establish a new identity to rescue Claire, Six is betrayed when Sosa demands money and is unexpectedly shot dead by Hansen, who arrives with his team. Six then sets a trap, flooding the cellar where Sosa is, leading to an explosive showdown and the death of Hansen’s men.
A brief but intense fight ensues between Six and Hansen, who is ultimately subdued when Miranda intervenes, tranquilizing Hansen. Miranda, however, is upset because she is being questioned about the operation by Carmichael, suggesting her own conflicted loyalties. She then traps Six in a trunk for his safety.
The story shifts to a mansion in Croatia where Hansen has kept Claire hostage, with Fitzroy being tortured in an attempt to get him to reveal information about Six. Despite brutal interrogation, Fitzroy refuses to betray him. Meanwhile, Six and Miranda visit the retired Margaret Cahill, played by Alfre Woodard, who reveals that the contents of the chip expose Carmichael’s corrupt dealings and abuse of power. As they escape a fierce attack by assassins sent after them, Cahill heroically destroys her own home along with the mercenaries inside to ensure the information is lost.
While on the run in Prague, Six and Miranda manage to uncover more about Carmichael’s illicit activities, but their pursuit becomes a dangerous game of cat and mouse. Cassandra’s team tracks them, resulting in more violence and chaos. A key moment occurs in a hospital where Six locates Claire using her pacemaker signals. This leads to a brutal confrontation with Lone Wolf, a mercenary sent after him, who tries to turn the police against Six.
Their relentless fight culminates in Croatia, where Six leads a daring assault to rescue Claire and confront Hansen once and for all. As they make their escape, Fitzroy sacrifices himself by detonating a grenade to give Six and Claire a chance to flee, dying heroically to keep them safe. Meanwhile, Miranda engages in a deadly fight with Wolf, resulting in Wolf surrendering the chip to her, recognizing Hansen’s true dishonorable nature.
The final showdown takes place in a hedge maze, with Hansen taking Claire hostage and bringing her to a fountain. Six drops his weapon to persuade Hansen to release Claire, leading to a brutal fight. Just as Six gains the upper hand, Brewer, revealing her own hidden agenda, shoots Hansen dead. She then shoots Six, attempting to cover up the true extent of corruption, and threatens Claire to keep him obedient, further complicating the web of deception.
In the aftermath, Carmichael and Brewer meet with higher authorities, trying to erase all traces of their wrongdoing by destroying the chip. They attempt to manipulate Six and Miranda into silence, but Six manages to escape custody, determined to protect Claire. The film ends with Claire, now in a secure, secret location, hearing gunshots and being reunited with Six, who then takes her away to ensure her safety and their future together, symbolizing hope amidst chaos.
> "Sometimes, you have to do terrible things to protect the people you love."
