The IMF team hijack the trade-off in Dubai between the assassin that killed Hanaway (Sawyer from Lost) in the first scene who has the launch codes, and Wistrom - the right hand man of Cobalt - who Brandt (Jeremy Renner) believes to be a crazy genius called Hendricks from a quick drawing with a biro that Ethan drew on his hand in a hurry.
The team meet both parties separately, assuming they've never met each other, and exchange the codes for diamonds. The plan backfires when Wistrom leaves with the real codes, while Jane Carter (Paula Patton) shoots and kicks the assassin out an open window from their skyscraper in retaliation for the murder of her true love. Ethan chases Wistrom - who turns out to be wearing a mask, and is really Hendricks, but loses him in a sandstorm.
Out of options, Ethan meets with Bogdan - the informant he broke out the Moscow prison, and a Russian arms dealer. To stop nuclear war, he learns that Hendricks is heading to Mumbai to use a satellite to launch the warhead from a Russian sub. As he leaves the arms dealer also tells the Russian agent Sidorov where to find Hunt.
The satellite is owned by an Indian playboy, so they gatecrash a party at his mansion. Carter lures him away to his private quarters - and then beats him up to get the security codes to override the satellite.
But it's too late -- Hendricks has taken the satellite offline, and instead used a relay from a TV tower to send the codes to the Russian sub. Ethan and Carter race through the streets to get to the TV station. They're let down by a dodgy sat-nav, and the warhead is launched towards the US.
Ethan spies Hendricks and gives chase through the streets of Mumbai. Wistrom destroys the broadcast building's equipment as he is chased by the other IMF team members. Carter is hit by a bullet. Wistrom cuts the power to the building, and Brandt is sent to take him out.
Meanwhile Ethan chases Hendricks to an I-Robot style carpark. They fight, but although Ethan can take down huge 'Stone Cold Steve Austin' style prisoners, he has trouble with this wily old man. Finally, having broken Ethan's leg, and with a broken arm himself, he jumps to his death - with the briefcase holding the remote device. To get it in time, Ethan dives into a car and plummets 100ft to crash next to the crazy scientist. He crawls out the wreck and opens the case.
Benji knows that Brandt is taking too long, so he goes to help out and shoots Wistrom dead, finally earning his badge. They turn back on the power, and Carter reboost the system.
Ethan presses the 'stop' button on the remote control with seconds to spare.
The missile, nearing the San Franciso tourist spots, suddenly flops a little in the air and crash lands into the ocean.
In the carpark, the Russian agent finally catches up to a damaged Ethan - and sees that he was telling the truth all along. He offers to take him to hospital.
A little while later, the team are brought together again - and finally we see Ving Rhames again! Ethan offers them all a new assignment (on iPhones again - a lot of Apple product placement in this one). Brandt doesn't accept. Ethan tells him that he knows he was on assignment in Croatia - but Brandt was set up so that Ethan could get into that Moscow prison. Brandt is emotionally quite calm and now accept the mission. What? As Lloyd christmas says, "All that pain and personal anguish - for nothing!!" So things are ok.
Ethan then sees his wife going for a drink with another man from work. He watches her. She turns around to see him from a distance. They wave. It's awkward. The other man wants a drink, so she just leaves and goes inside the restaurant. Ethan heads off to work again.