In 1999, Tony Stark attends a New Year’s Eve celebration at a lavish scientific conference where his arrogance and self-indulgence are on full display. There he meets Aldrich Killian, a socially awkward and physically disabled scientist who pitches Stark on joining his think tank, Advanced Idea Mechanics. Stark mockingly pretends to be interested, sending Killian to wait for him on the rooftop while having no intention of showing up. Instead, Stark spends the night with brilliant botanist Maya Hansen, who demonstrates an experimental regenerative project called Extremis—a form of genetic manipulation capable of healing injuries and rewriting biological tissue. As fireworks ring in the new millennium, Killian remains abandoned on the rooftop, humiliated and resentful.

Thirteen years later, following the Battle of New York, Tony has become deeply traumatized by his near-death experience carrying a nuclear missile through the wormhole. He suffers panic attacks, insomnia, and obsessive anxiety, coping by building dozens of Iron Man suits in his workshop. While Tony struggles privately, the world faces a new public threat: a mysterious terrorist known as the Mandarin, who claims responsibility for a series of bombings marked by no forensic evidence. To reassure the public, the U.S. government rebrands James Rhodes’ War Machine armor as the patriotic “Iron Patriot.” When Tony meets Rhodey at a diner, a child asks about the wormhole incident, triggering another panic attack and revealing how badly Tony has been affected.

At home, Tony’s relationship with Pepper Potts becomes strained as his emotional instability worsens. One night, one of Tony’s automated suits nearly attacks Pepper after reacting to his distress during a nightmare. Matters become more complicated when Aldrich Killian reappears, transformed into a handsome, confident businessman with no trace of his former disability. He invites Pepper to join AIM, but she declines. Meanwhile, Happy Hogan, now Stark Industries’ head of security, becomes suspicious of Killian’s bodyguard Eric Savin and follows him to the Chinese Theatre. There, Happy witnesses veteran Jack Taggart suddenly erupt in a massive explosion, destroying the area and leaving Happy gravely injured. Savin, despite suffering injuries of his own, mysteriously regenerates and escapes.

Enraged after visiting Happy in the hospital, Tony publicly challenges the Mandarin on live television and recklessly gives out his home address. Soon afterward, Tony is visited by Maya Hansen, who warns him about Extremis. Before they can talk further, Stark’s Malibu mansion is attacked by helicopters under the Mandarin’s command. The house is destroyed, but Pepper saves Tony by forcing him into the prototype Mark XLII armor. Tony is launched away from the collapsing mansion and, due to a preprogrammed flight path, crashes in rural Rose Hill, Tennessee. With the suit nearly powerless and the world believing him dead, Tony is stranded with no resources.

Using his apparent death as cover, Tony investigates one of the Mandarin bombings that was never publicly claimed. He befriends a clever local boy named Harley Keener, who helps him recharge his suit and gather clues. Tony discovers that the bombings are not conventional explosives at all—they are failed Extremis subjects whose unstable bodies overheat and detonate. He is attacked by Extremis operatives Ellen Brandt and Eric Savin, but defeats them using improvised weapons and escapes. Tony realizes that all roads lead back to AIM and to Killian. Pepper also learns from Maya Hansen that Killian has perfected and weaponized Extremis, but before they can act, Killian kidnaps Pepper.

Tony tracks the Mandarin to a lavish mansion in Miami and infiltrates it using homemade gadgets. There he discovers the shocking truth: the feared terrorist is actually Trevor Slattery, a clueless British actor hired to play the role of the Mandarin for propaganda videos. Killian created the fake villain to cover up failed Extremis experiments and manipulate world events through fear. Tony learns that Killian used Extremis to cure his own disabilities and then tested it on wounded veterans, whose fatal explosions became the Mandarin’s so-called attacks. When Maya threatens to expose him, Killian murders her and reveals he has subjected Pepper to Extremis as leverage against Tony.

Killian also manipulates U.S. intelligence to lure Rhodey and seize the Iron Patriot armor. Using Eric Savin inside the suit, he launches an assault on Air Force One and kidnaps President Matthew Ellis. Tony intercepts the attack and heroically saves passengers sucked from the damaged plane, but Ellis is captured. Tony reunites with Rhodey, and together they trace Killian to an offshore container terminal where he plans to execute the President live on television. Vice President Rodriguez is revealed as Killian’s accomplice, willing to help in exchange for Extremis to cure his disabled daughter.

Tony and Rhodey launch a final assault on the terminal. Tony summons the “Iron Legion,” an army of remote-controlled Iron Man suits, while Rhodey rescues President Ellis. Tony finds Pepper alive, transformed by Extremis, but before he can free her the structure collapses and she appears to fall to her death. Tony then battles Killian using multiple suits, eventually trapping him in one and detonating it. Killian survives due to Extremis and proclaims himself the true Mandarin, but Pepper—also empowered by Extremis—returns and kills him.

In the aftermath, Tony orders J.A.R.V.I.S. to destroy all of his suits in a symbolic gesture known as the Clean Slate Protocol. Pepper is cured of Extremis, and Tony undergoes surgery to remove the shrapnel near his heart, freeing himself from dependence on the arc reactor. He rewards Harley Keener for helping him and returns to the remains of his mansion, throwing the old arc reactor into the sea. Declaring that the armor was never what made him a hero, Tony states that no matter what he loses, he will always be Iron Man.

The story then cuts to reveal Tony has been narrating these events to Bruce Banner as a form of therapy. Unfortunately, Banner fell asleep early in the tale and admits he is not qualified to help, prompting Tony to begin telling the story all over again.