Confirmed by multiple folks across the internet. I've compliled this from multiple sources, including the now-deleted comments from IMDB. The final act is missing some stuff, like how two major characters get from one ship to another, and might have some stuff out-of-order, but all the major bits are there.
If you don't want to be spoiled, DO NOT READ BELOW THIS LINE.
IMAX preview is reversed in final film; Nibiru first, then London attack.
Nibiru: Kirk violates Prime Directive by taking the Enterprise into the volcano, and for all the locals to see to save Spock.
London: Harrison offers to cure Starfleet agent's terminally ill daughter, but at a price. Triggers a bomb at the Starfleet Data Archives.
Kirk and Spock @ Starfleet headquarters, expect to get 5-year mission, but instead due to their conflicting reports about Nibiru (Kirk lied, Spock told the truth), Kirk is removed from captaincy for Prime Directive violation on Nibiru on orders of Admiral Marcus. Pike re-assumes command of Enterprise. Spock assigned to another ship.
Kirk goes to get drunk, Pike offers emotional support and first officer post on Enterprise. "I believe in you Jim" scene from trailer.
Starfleet brass meeting about London attack. Kirk wonders why Harrison would attack, and seems to have lost some of his confidence as Marcus has to push him to get the full answer. Kirk speculates the attack was a ruse to get the brass together… and surprise, Harrison shows up, shoots up the place wounding Pike and others. Kirk shoots back, Harrison beams out. Spock melds with Pike, Pike dies. Kirk visibly shaken (father/son relationship stressed with Kirk/Pike). Kirk asks Marcus for permission to go after Harrison, who has fled to Qo'nos.
Marcus gives Kirk advanced torpedoes along with a weapons specialist (nee cute blonde lab technician) named Carol Wallace. Scotty won't let the torpedoes on board, because they're shielded and he cannae scan them. Kirk, blinded by vengeance (ha!), overrides him and promotes Chekov to Chief Engineer (go get a red shirt!). Scotty leaves Enterprise. Enterprise warps to Qo'nos.
Leaving Sulu in command on Enterprise, Kirk and co. go down to Qo'nos, and eventually get cornered by the Klingons. Harrison comes swooping in (literally), and takes all the Klingons out. Kirk tries to engage Harrison in hand-to-hand combat, but Harrison does not react. Meanwhile, McCoy and company try to open one of the torpedoes only to discover it is a cryotube containing a frozen humanoid.
Kirk arrests Harrison, all beam back to Enterprise. Spock does some homework, and discovers Carol Wallace is actually Carol Marcus; Wallace is her mother's maiden name. Enterprise confronted by USS Vengeance; Admiral Marcus in command. Marcus orders Kirk to hand over Harrision, but Kirk does not trust him. Marcus attacks Enterprise, Kirk offers himself for the lives of his crew, Marcus declines. Carol pleads her father to stop; he beams her aboard. Suddenly, USS Vengeance powers down; Scotty is aboard Engineering and contacts Kirk.
Kirk interrogates Harrision. Harrison reveals he is Khan; Section 31 found the Botany Bay, revived Khan, and kept the remainder of Khan's crew in stasis as a bargaining chip to get Khan to do as ordered. McCoy takes a blood sample from Khan.
Kirk and Khan spacejump to USS Vengeance from Enterprise, where Scotty lets them onboard. Spock calls Spock Prime on New Vulcan and asks about Khan; Spock Prime cautions that although he promised never to reveal anything about their lives, he can confirm that Khan is dangerous, and subduing him in the prime universe came at "great cost".
Khan assumes command of Vengeance from Marcus, and demands the torpedoes / cryotubes Kirk has on Enterprise. Meanwhile, McCoy does some testing with Khan's blood on a dead Tribble.
Warp speed battle ensues back to Earth. Khan decides to ram his dead ship into Starfleet Command; both Vengeance and Enterprise fall from orbit. Very TWOK here: Kirk goes to Enterprise engineering with Scotty to bring the warp core back online (instead of Spock in TWOK), and dies in the process, saving the Enterprise and his crew. In sickbay, McCoy notices that the Tribble has come back to life after the infusion of Khan's blood, figures it'll work for Kirk, and Spock beams down to Earth to chase down Khan and get a bigger sample of blood to save Kirk. Spock and Khan battle throughout San Fran and on a flying ship, with Khan continually beating Spock down, but Spock keeps getting back up. Uhura shows up, and stuns Khan over and over until they both have him subdued.
Several weeks later, Kirk awakes in hospital. Flying jets scene from trailers as Kirk, Spock and crew receive their five-year mission.