The movie begins with Dom Cobb (Leonardo DiCaprio) lying face down on a beach. Some security guards take him to a Japanese-style castle, where he meets an old man. The old man and Cobb have a brief conversation about how familiar they look to one another.
The movie then cuts to Cobb and his associate Arthur (Joseph Gordon-Levitt) having a business meeting with Saito (Ken Watanabe). Cobb and Arthur are trying to convince Saito that they can help prepare his mind from being invaded by "extractors" who steal ideas while their targets are asleep. Cobb and Arthur see Mallorie (Marion Cotillard), Cobb's wife, even though she's dead. Cobb has been projecting Mallorie into various dreams.
Eventually, Saito tells Cobb and Arthur that he realizes that they've invaded his subconscious. After a brief shootout, all three wake up in what appears to be a South American country filled with rioters. This is also a dream, so the previous business meeting was a dream-within-a-dream. The reality is that Cobb, Arthur, and another person have induced Saito into sleeping/dreaming on a train in Japan. Cobb, Arthur, and their associate wake up before Saito and walk away from Saito, leaving Saito alone on the train.
Cobb sits in a hotel room, where he receives a phone call from his kids. He explains that he can't go home to them for a while. Arthur and Cobb then go to the rooftop to a helicopter to leave Japan. They are surprised to see Saito in the helicopter. It turns out that Saito was testing their skills and wants to hire them for a job. He wants them to plant an idea ("inception") in a business rival's mind. Saito wants Robert Fischer (Cillian Murphy), the son of another industrialist, to dissolve his business empire. Otherwise, Fischer will control more than half of the world's energy supply.
Cobb goes to Paris to recruit a new architect of dreams. He visits Michael Caine's character, who's an architecture professor. They recruit Ariadne (Ellen Page). Cobb and Arthur show her how to create dream environments. They also establish some rules and practices. For example, Cobb and Arthur have "totems", which are items that they use to help them tell that they're back in reality. Cobb uses a spinning top. The top spins continuously in a dream world, but in the real world, the top stops spinning due to gravity. Arthur uses a loaded die. Ariadne makes her totem out of a bishop chess piece. Cobb also recruits Eames (Tom Hardy), who's good at using weapons and impersonating other people once inside target's dreams, and Yusuf, a pharmacist who creates chemicals to induce deep sleep.
It's easier to explain some of the "ground rules" first before continuing with the story.
There are two main ways to wake up from a dream. One way is to have a "kick" initiated by the sensation of falling. The other way is to die.
Unfortunately, if you're in a deep sleep, dying in a dream is not a good idea. You could be stuck in mental limbo for a long time, possibly until your body dies for real in the real world.
A target's subconscious projections are naturally suspicious of intruders. A well-trained mind will have defenses against intruders. Robert Fischer has been prepared by mental strategists, so his subconscious creates bodyguards who try to kill Cobb and his team.
Since time passes quicker in dreams than in reality, an hour of dreaming can feel like several days have passed.
Even though they're usually in someone else's subconscious, everyone keeps seeing Mallorie if Cobb is inside a dream with them. Cobb is unable to keep his memories of Mallorie compartmentalized.
Cobb, Arthur, Saito, Eames, Ariadne, and Yusuf board a plane from Sydney to Los Angeles. This is one of the longest commercial flights in the world, which allows the team ample time to plant an idea deep within Robert Fischer's subconscious. "Inception" is difficult because a mind is good at rejecting foreign ideas.
Here are the dream layers during this part of the movie: Layer 1: Everyone goes into a generic city. Cobb and his team abduct Robert Fischer. Saito is shot in this dream layer, but because they are in deep sleep, Cobb says that killing Saito won't cause him to wake up. Saito might just stay in limbo.
Layer 2: Yusuf remains awake in Layer 1. He drives a van. Everyone else, including Fischer, is put into yet another dream layer. Layer 2 takes place in a hotel. Cobb tells Fischer that his mind has been invaded and that he (Cobb) is trying to help Fischer fight off the invaders. As the van in Layer 1 is attacked and eventually starts falling into a river, gravity is disrupted in Layer 2. Saito coughs up blood in Layer 2 even though he's not hurt in Layer 2.
Layer 3: Arthur remains awake in Layer 2 as he fights off Fischer's subconscious bodyguards. Everyone else goes into Layer 3, which has everyone trying to get inside a fortress on top of a snowy mountain. Cobb tells Fischer that Fischer's father has a secret will that has special instructions about how to handle his business empire. Cobb's hope is that, this deep in Fischer's subconscious, Fischer will think that dissolving the business is his idea. However, Fischer is shot and killed in Layer 3. Again, Saito coughs up blood even though he's not hurt in this layer.
Layer 4: Cobb and Ariadne go into Layer 4 to find Fischer, who's now in limbo having died in Layer 3. In Layer 4, Cobb finally explains to Ariadne what happened to Mallorie. Many years ago, Cobb and Mallorie went into deep sleep. They spent around 50 dream years together, and Mallorie didn't seem to want to leave. Therefore, Cobb planted an idea in her subconscious that they had to return to reality. Unfortunately, once back in reality, Mallorie never believed that they had returned to reality, so she killed herself by jumping off a building. Cobb has been wracked by guilt all this time. He cannot return to the U.S. because they authorities think that he killed Mallorie.
Ariadne finds Fischer in limbo and goes back to Layer 3 with him. Cobb stays in limbo to find Saito, who has also died in Layer 3. Back in Layer 3, Fischer finally walks into a room where he thinks he sees his dying father. He opens a safe, which presumably has a will that tells Fischer that he should break up his company.
The movie now returns to its opening images. Cobb is eating dinner with the old man at the beginning of the movie. The old man is Saito, who's been trapped in limbo for a long time (remember, dream time passes faster than real time).
There is a montage of all the "kicks" happening as the characters wake up from the various layers of dreams.
The movie then cuts to all of the characters waking up on an airplane. Saito makes a phone call, and the characters all walk through immigration without being arrested. Cobb is picked up by Michael Caine's character, and they go to a home where Cobb's kids are playing. They are wearing the same clothes that Cobb usually dreams of them wearing. Cobb spins the top on a table before going to play with his kids in the yard. The last shot of the movie is of the spinning top, which spins for a very long time.
The movie cuts to black while the top is still spinning, however, there is a slight wobble just as the film ends. Is he back to reality?
*CUT TO THE CHASE*
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From Curt: Cobb (Leonardo DiCaprio) and his team specialize in a very unique type of corporate espionage-"extraction," or the invasion of their targets' dreams to steal ideas and secrets from their subconscious minds. They are approached by Saito (Ken Watanabe), who wants to hire them to do something that is thought to be impossible-"inception," or implantation of an idea into the subject's mind. Cobb agrees to take on the challenge, but only because Saito offers him the one thing in the world he wants: to be reunited with his children.
As the caper (which involves four levels of nested dreams intended to convince Fischer (Cillian Murphy) that he has independently formulated the notion to break up his father's business empire) proceeds, it is revealed that Cobb has done inception before, and that the idea he inadvertently implanted in his wife Mal's (Marion Cotillard's) subconscious led to her eventual suicide.
The mission appears to be successful in all respects, but as Cobb returns to his home and embraces his children, the final shot of the film shows Mal's metal top spinning on and on, hinting that Cobb, after all, may not have successfully returned to "reality."
Just before the film cuts to black, the metal top begins to wobble, which indicates that this is not a dream, confirming that Cobb was successful in his mission, and is in reality, reunited with his family.
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