Plot
In 2092, humanity has conquered mortality. The world watches as 118-year-old Nemo Nobody, the last mortal, approaches death. Psychiatrist Dr. Feldheim uses hypnosis to help Nemo remember his life. A journalist also interviews Nemo, whose recollections are from three points in his life: ages 9, 15, and 34. Nemo makes contradictory statements, describing his past as having unfolded in multiple ways. He says that, before birth, children know everything that will happen in their lives, but at the moment of conception the Angels of Oblivion erase the knowledge. He says the Angels missed him, allowing him to "remember" his different possible futures.
After his parents' divorce, 9-year-old Nemo had to choose whether to live with his mother or his father. He describes what happened in both scenarios.
Life with his mother
Nemo and his mother move to Montreal. When he is a teenager, he is attracted to Anna. At the beach, Anna asks Nemo to swim with her and her friends. He insults her friends, and they hardly see each other again.
In an alternate timeline, Nemo admits to Anna that he cannot swim, and they spend time together. Anna's father Harry marries Nemo's mother, and the step-siblings begin an affair, pledging their lives to one another. Harry and Nemo's mother divorce, and Anna goes to New York with her father. The teenagers lose touch. Years later, Nemo and Anna pass at a train station and immediately recognize each other. After a passionate reunion, Anna says she is not ready for a relationship. She asks Nemo to call her and meet at a lighthouse, but he loses her number. Nemo waits at the lighthouse every day, but Anna does not come.
In another timeline, Anna and Nemo are married with children. He works at a television studio. Driving home, he loses control of his car, plummets into a lake, and drowns.
Life with his father
As a teenager, Nemo lives in England with his disabled father and is writing a science fiction story about a journey to Mars. He falls in love with Elise, whose boyfriend is 22-year-old Stefano. Nemo has a motorcycle accident and is hospitalized in a vegetative state or pseudocoma. He can still perceive the world and detects his parents' reunion at his bedside. He imagines his fingers on his typewriter keyboard and continues working on his story.
In another timeline, Elise says she is in love with Stefano, but he does not love her. Nemo assures her of his feelings until she gives in, and they marry. In one version of this timeline, Elise dies in an explosion on their wedding day, and Nemo takes her ashes to Mars as he had promised when they were teenagers. On the way back to Earth he meets Anna, but the ship is destroyed by asteroids. In another version, one of Nemo's television studio coworkers drowns in the lake. Their widow is Anna, whom Nemo feels he has seen before. Another timeline has Nemo and Elise married with three children. Elise has borderline personality disorder and chronic depression and, despite Nemo's attempts to save their marriage, leaves him to pursue Stefano.
Alternately, after being rejected by Elise, teenage Nemo resolves to marry the first girl who dances with him, who turns out to be Jean. Though they marry, have two sons, and become rich, Nemo is bored and puts all of his assets in Jean's name and leaves. Making decisions via coin toss, he claims to be the person for whom a chauffeur is waiting. He is taken to a hotel where he is murdered and his body is dumped in the woods by the assassins, who question whether they have killed the right man.
Adult Nemo also repeatedly awakens in a surreal environment dominated by argyle patterns. Following clues that he finds in this world, he arrives at a dilapidated house with a DVD player and television. In an interactive video, 118-year-old Nemo tells 34-year-old Nemo that this is a universe where Nemo was never born, and his consciousness is stuck in limbo. Old Nemo states that he is experiencing the story from the end, and that adult Nemo must stay alive until 5:50 a.m. on 12 February 2092.
In epilogue, Old Nemo tells the journalist that neither of them exists — they are figments of 9-year-old Nemo's imagination as he struggles to choose between his parents. The boy is trying to choose by tracing the potential outcomes. He takes a third option: leaving both parents for an unknown future.
Near death, Nemo recalls reuniting with Anna at the lighthouse. The moment of his death arrives, and his last word, "Anna", is broadcast. The universe ceases to expand and begins to contract. The flow of time reverses, old Nemo comes back to life and cackles joyously. The other Nemos come back to life and Nemo's parents get back together. 9-year-old Nemo runs in reverse to 9-year-old Anna and they reverse-skip stones together.