At a German concentration camp in Poland during 1944, a young Erik Lensherr (Michael Fassbender) experiences a traumatic separation from his parents at the hands of Nazi guards. In a moment of sheer desperation, the boy remarkably bends a metal gate with his mind until a guard forcefully knocks him unconscious. Observing from a distance is scientist Sebastian Shaw (Kevin Bacon), who summons Lensherr to showcase his powers further. Shaw cruelly orders Erik to move a coin; upon his failure, Shaw exacerbates the situation by executing Lensherr's mother right before his eyes. Consumed by rage, Erik unleashes his devastating magnetic abilities, resulting in the death of the guards and catastrophic destruction—much to Shaw's twisted delight.
Meanwhile, in Westchester County, New York, a young Charles Xavier (James McAvoy) encounters a shape-shifting girl known as Raven (Jennifer Lawrence). Disguised as his mother, Raven is rummaging through the fridge for food when Charles, using his telepathic gifts, communicates with her. Upon revealing her true blue-skinned form, they forge a bond as two unique individuals, with Charles inviting her to live with his family.
Fast forward to 1962 in Switzerland, Erik’s quest leads him to confront a banker, where he violently extracts information about Nazi gold's location in Argentina. In a tavern there, surrounded by former German soldiers, Erik unleashes his fury, killing three in his relentless pursuit of Shaw, ultimately discovering that Shaw is docked in Florida.
Meanwhile, in England, Xavier is advancing his research on mutation at Oxford University while navigating a complicated relationship with his foster sister Raven, who harbors feelings for him but feels rejected due to her appearance.
In Las Vegas, CIA agent Moira MacTaggart (played by Rose Byrne) infiltrates the Hellfire Club, where she witnesses Shaw and his dangerous cohorts—Emma Frost (January Jones), Riptide (Alex Gonzalez), and Azazel (Jason Flemyng)—threatening Colonel Hendry. Shaw's manipulation becomes clear as he exerts pressure on Hendry to adjust his stance on nuclear missile installation in Turkey, a threat underscored by Riptide’s terrifying display of power, hurling Hendry into a wall when he hesitates to comply.
Determined to expose Shaw and his mutant threat, MacTaggart seeks Xavier’s expertise on mutations. Together they strategize a plan to track down Shaw, just as the villain prepares to launch a nuclear war between the U.S. and Russia, hoping to eradicate humanity. The tension escalates when Xavier and Erik confront Shaw on his yacht. Despite Erik's intentions, Shaw's cunning tactics result in a fierce showdown, revealing the depth of their conflict.
As the two factions clash, Xavier and Lensherr gather a team of mutants, including Hank McCoy (Nicholas Hoult), leveraging a prototype Cerebro to hone their powers against Shaw's growing influence. The stakes reach a tipping point when Shaw's plans result in devastating confrontations. The conflict culminates in an epic confrontation where Lensherr, now fully embracing his identity as a mutant, must decide the fate of both his and Xavier's ideals.
In a final, heart-wrenching confrontation at sea, Lensherr’s choice to exact vengeance leads to irrevocable consequences, resulting in fractured alliances and a redefined future for mutants as he embraces his new identity as Magneto, forever altering the path ahead.
