The X-Men, mutant heroes sworn to defend a world that hates and fears them, must face evolution itself in the shape of their former teammate, Jean Grey (Famke Janssen). Possessed with the cosmic power of the Dark Phoenix, the resurrected Jean Grey has become a danger to herself, her mutant comrades and the entire planet. To stave off this imminent threat to humanity, a potential cure is discovered and processed to treat and ultimately eliminate genetic mutations once and for all.

As the battle lines are drawn, the X-Men, led by Professor Charles Xavier (Patrick Stewart), are aided by new recruits like The Beast (Kelsey Grammer) and Angel (Ben Foster). Together, they must contend with Greys new powers, as well as the malevolent Brotherhood a band of powerful mutants organised under Xaviers former all, Magneto (Ian McKellen).