In the future, robots known as Sentinels are exterminating mutants and their human allies. The Sentinels are near invincible as they possess Mystique’s powers of transformation. This technology was made possible following research performed on Mystique when she was captured during the assassination of Dr. Bolivar Trask, creator of the Sentinels. A band of mutants, including Kitty Pryde, Colossus, Iceman, Bishop, Warpath, Blink and Sunspot, convene with Wolverine, Storm, Professor Charles Xavier, and Magneto in a hideout in remote China. Pryde sends Wolverine’s consciousness back fifty years to 1973 to prevent Mystique from assassinating Trask, which led to her capture and revealed the threat that mutants could pose to normal humans.
At the X-Mansion in 1973, the future/present Wolverine encounters Xavier and Hank McCoy. Xavier, a broken man, has been overusing a serum that allows him to walk but suppresses his telepathy. Wolverine explains his mission and persuades Xavier to help free Magneto from a prison cell beneath The Pentagon, where he is being held for assassinating President John F. Kennedy. They rescue Magneto with the help of Peter Maximoff, a mutant with super speed.
In Washington, D.C., Trask unsuccessfully tries to sway Congress to gain support for his Sentinel program. Meanwhile, in Saigon, Mystique prevents William Stryker from appropriating a group of mutant G.I.s for Trask’s research.
Xavier, Magneto, Beast, and Wolverine fly to Paris to intercept Mystique, who is impersonating a North Vietnamese general to infiltrate the Paris Peace Accords. However her presence is discovered as Trask endeavors to demonstrate the Prototype Sentinel technology to military leaders. The group arrives as Mystique is about to kill Trask. Magneto tries to kill Mystique to ensure her DNA cannot be used for the Sentinels, but she escapes. The fight spills onto the street in view of the public, allowing Magneto and Mystique to escape.