Maxwell "Max" Smart (Steve Carell), an analyst for the top-secret American intelligence agency, CONTROL, yearns to become a field agent like his idol, Agent 23. Despite his amazing scores in the acceptance tests, Max is denied the promotion because the Chief (Alan Arkin) of CONTROL feels that Max's analytic skills are best used for his present assignment. When CONTROL headquarters is attacked by the terrorist organization KAOS, led by Siegfried, almost all of CONTROL's agents' identities are exposed, leaving only Max and Agent 99 (Anne Hathaway), to pursue the culprits while former field operatives are demoted to desk jobs. Max is promoted to field agent as Agent 86, but the experienced 99 is reluctant to partner with him because of his clumsy personality.Max and 99 enter Russia by parachute, hoping to trace KAOS' recent acquisition of nuclear materials through its chief bomb maker, Krstic. Along the way, they are attacked by Dalip, one of Siegfried's henchmen. By infiltrating a luxurious party hosted by Krstic, they trace the nuclear material to a KAOS nuclear weapons factory disguised as a Moscow bakery, but when Krstic and his men corner them, Max is forced to shoot him. In the bakery, Max meets with Siegfried and his second-in-command, Shtarker, only to learn that Siegfried was expecting him because a double agent has compromised his and 99's identities.Max manages to escape capture and destroy the weapons factory, but during their escape, Max and 99 are confronted by Dalip. Realizing that he knows Dalip through hours of listening to him on spy 'chatter', Max manages to persuade Dalip to spare their lives. The Chief sends 23 (Dwayne Jhonson) to observe the clean-up of the factory, but KAOS manages to sneak the weapons out through the Moskva River, with 23 reporting that only a bakery has been destroyed. Realizing that Max was alone during his key discoveries, CONTROL believes Max to be the double-agent. 99, who has been gradually falling in love with Max, is heartbroken but takes Max into custody.CONTROL's warning is disregarded when Siegfried threatens to release nuclear weapon detonator codes to hostile countries unless the United States government pays him $200 billion. KAOS plans to plant a nuclear bomb in Los Angeles. While Max is in a CONTROL holding cell, Dalip sends him a coded message via the radio show American Top 40 revealing Siegfried's plan.Max escapes from CONTROL and steals the original red Sunbeam Tiger roadster from the TV show but quickly runs out of gas. While attempting to find a vehicle, Bernie Kopell, the original Siegfried (driving an Opel GT), is rear-ended by another car while yelling at Max not to stand in traffic. Max commandeers a blue Volkswagen Karmann Ghia (another original car from the TV show), then gets a ride on an Air Force fighter jet, arriving in Los Angeles to unite with the Chief, 99, and 23, who have flown out to persuade the President to take the KAOS threat seriously, while a decoy distracts a SWAT team.Max manages to convince 99 and the Chief that he is not the double-agent. As KAOS plants the nuclear bomb in the Walt Disney Concert Hall, where the president will be attending a concert, the group figures out that 23 is the real double-agent after Max's Geiger counter-equipped watch beeps when he is near 23, picking up trace elements of radiation. 23 then pulls out a gun, takes 99 hostage and flees in a government-issue black GMC Yukon Denali SUV.Max and the Chief commandeer another government car (a Cadillac DeVille) and pursue 23 before crashing into a golf course. The car hits a shack, sending it flying through the air, and landing on the fence of an airport which allows Max and the Chief to hop onto a small plane. Max reaches 23's car by jumping out of the plane and rescues 99, but in the struggle, the car is set on fire and forced onto railroad tracks. Max then kisses 23 to distract him. The SUV collides with a freight train, killing Agent 23.After analyzing 23's nuclear football, Max realizes that the bomb will be triggered by the final note of Beethoven's "Ode to Joy". They rush to the Disney Hall, with Max tackling the elderly conductor just before the final note, saving the president and Los Angeles. Siegfried, after finding out that his plan has failed, informs Dalip that he will not kill Dalip's wife for his failure since he did do his job but arrogantly remarks that it would do the world a favor if he did so. In response, Dalip throws Siegfried into a river, which also elated Shtarker.Back in CONTROL headquarters, a new "employee" is teased and harassed by Larabee and Agent 91 until they discover that he's Hymie, a CONTROL robot built by nerdy techies Lloyd and Bruce. Max is afterwards given honors and gets his dream of becoming a real spy with agent 99 as his girlfriend, while Dalip becomes an analyst of CONTROL. The movie ends as Max and 99 exit CONTROL headquarters through the walkway.