Cobb and Ariadne descend into a fourth layer of the dream: a crumbling cityscape that Cobb and Mal built together in the fifty years they spent in "limbo."
Cobb confesses to Ariadne that he "incepted" the idea in Mal that limbo was not real, so that she would agree to wake up and be with their children; however, Mal continued to believe that reality was a dream, and eventually committed suicide, leaving Cobb ridden with guilt.
In a nearby building, Ariadne and Cobb find Mal and Robert, whom Ariadne wakes up so that he can infiltrate the fortress's "strong room."
Robert inputs a code in the strong room that reveals a large operating room with his dying father inside. Robert's father tells him to live his own life, rendering the inception complete.
As the dreamworld collapses, Cobb tells Ariadne to ride the "kicks" up through the layers of the dream while he rescues Saito.
Cobb washes up on a shore and is dragged into Saito's house, just like in the film's opening scene.
Cobb eventually finds an elderly Saito who has been waiting in limbo for decades in dream time (just a few hours in real time), and the two help each other to remember their arrangement.
The two of them suddenly wake up on the passenger airliner next to Ariadne, Robert, Eames, and Saito, who have all successfully made it back to reality.
Cobb arrives in the United States and is greeted by Stephen Miles, who takes him to his children.
Cobb arrives home and goes outside to play with his children, while his totem continues to spin.