Lights, camera, action!
Cobb is just hanging out on a beach with his kids...by which we mean he's half-drowned, hallucinating, and apparently washed up in some hostile territory.
It's not looking too good for ol' Cobb. He begins talking to a very elderly Japanese man. This guy starts to tell him a memory that we follow back into the past. Hold on to your hats—things are about to get confusing.
Cobb and his buddy Arthur are trying to take something from the Japanese guy (named Saito), but he's onto them. Cobb's wife, Mal, is there for some reason; she says some strange things and betrays them.
Then they wake up.
Then they wake up again.
Huh?
That's right: not only was the whole thing a dream, it was actually a dream within a dream. Cobb and Arthur were trying to extract information from Saito (but failed), so now they're on the run. Apparently what they're doing isn't legal, and the company they work for doesn't take kindly to failure.
Saito appears again: apparently the whole thing was a test. Cobb is estranged from his kids, and Saito can help him return if Cobb pulls off an "inception," i.e., placing an idea in someone's mind and making them think it's their own.
Arthur says that inception is impossible—but Cobb is game.
Now it's time for him to assemble a crack team of dream invaders.
First Cobb gets Ariadne, an architect from a French university, whose job is to build the dreams. Then he meets with a forger (who impersonates people) named Eames. Eames introduces Cobb to a chemist to apply the necessary sedation.
This crack team of dream-criminals still needs a plan.
Enter: montage.
They want to subconsciously repair the relationship of a son and his father so that the son will dissolve the father's company. (Yeah, maybe that sounds a little counter-intuitive, but just work with us here. Brief summary and Inception don't exactly go together.)
With the plan in motion, they set off… and run into a bunch of gunmen. It looks like Fischer, their mark, has had some dream defense training and now their impossible job gets even more impossible.
So they capture Fischer and escape the projections (subconscious people that Fischer populates the world with), and Eames imitates Browning (a right hand man of Fischer senior) to try to turn Fischer against Browning and toward his father.
Now it's time for Dream #2, which is a bit trickier.
The only way to proceed is to turn Fischer against his own subconscious by making him realize it's a dream. Cobb does this (and it kinda works), but they're still on a very short clock, so they jump right into a third level dream by convincing Fischer he's going to explore Browning's dream and find out his secrets.
Ariadne has decided that the third dream level should be a military fortress in an inhospitable snow-scape…nice thinking. Anyway, they all work to try to get Fischer to the safe room where a projection of his father is waiting for the final inception.
Remember Cobb's projection of his wife Mal, though? She's still having fun betraying her husband, so she shoots and kills Fischer. Then Ariadne and Cobb go into Limbo (the land of "pure subconscious") where they confront (and defeat?) Mal and save Fischer. Cobb stays to save Saito (who had been shot and eventually died and ended up in Limbo).
They all wake up on the airplane where they were dream-sharing with Fischer. Saito makes a call, and Cobb is able to make it through immigration and finally see his kids again.
Or...is Cobb still dreaming?