In 2092, humanity has conquered mortality through the endless renewal of cells. The world watches in fascination as the 118-year-old Nemo Nobody, the last mortal on Earth, edges towards death. Curious to know of life before quasi-immortality, they interview Nemo. Dr. Feldheim, a psychiatrist, uses hypnosis to help Nemo recall some of his memories, while Nemo relates other memories to a journalist. As he is prodded, Nemo makes contradictory statements. He recounts his life at three primary points: at age 9, when his parents divorced, at age 15 when he fell in love, and at age 34 as an adult. All three unfold into their many possible outcomes.
Nemo explains that before birth, children remember everything that will happen in their lives. At the moment of conception, the Angels of Oblivion erase their memory. The Angels, however, forget about Nemo, allowing him to “remember” different possible futures for himself. At age 9, at a railway station, he is forced to choose as his mother leaves on a train while his father stays on the platform. In one case, he manages to board the train while in another he stays with his father.
A rebellious Nemo lives with his mother and her new partner, Harry, in Montreal. He sees a new girl, Anna, in his school and is immediately smitten. One day on the beach, Anna asks if he would like to swim with her and her friends. Nemo insults her friends and they barely see each other again.
In an alternate story line, Nemo admits to Anna he cannot swim; the two spend time together and fall in love. Anna turns out to be Harry’s daughter and the two step siblings begin an affair. They pledge their lives to one another. When Harry and Nemo’s mother break up, Anna goes to New York with her father, and they lose touch. Years later, Nemo works as a pool cleaner, hoping to run into Anna by chance. They finally see one another at the train station and immediately recognize each other in a crowd of passers-by. After a passionate reunion, Anna announces she is not ready to immediately resume the relationship. She gives him her number, asks him to call her in two days and meet at the lighthouse. However, he loses her number when a sudden downpour makes her note illegible. Nemo waits at the lighthouse every day, but Anna does not come.
In a different storyline, Anna and Nemo are married with children. Nemo works at a television studio narrating educational videos. One evening, while returning home, he hits a bird, loses control of his car, plummets into a lake and drowns.
Nemo stays with his father, who later becomes disabled. He works in a shop and spends his free time at home at the typewriter, writing a science fiction story about a journey to Mars. At a school dance, he meets Elise and falls in love. A few days later, Nemo goes to Elise’s house but sees her with her 22-year-old boyfriend. Frustrated, he speeds away on his motorcycle, has an accident and is hospitalized in a vegetative state. Though he can perceive the world through his senses, Nemo cannot move or speak. He detects his parents’ reunion at his bedside. Nemo tries to remember the movement of his fingers on the typewriter keyboard and eventually manages to lift a finger as this story line comes to a close.
In yet another alternate timeline, Nemo speaks with Elise at her house, and learns that she is still in love with her boyfriend, Stefano. Nemo does not back down and keeps assuring her of his feelings. Finally, Elise gives in and a few years later, they get married. In one version of the story line, Elise dies in an accident on the return from the wedding. Nemo keeps her ashes, having promised her to spread them on Mars. In a far future, Nemo carries Elise’s ash to Mars and spreads them on the planet’s surface. Aboard the spacecraft traveling back to Earth, he meets Anna. Before they can say much to each other, the ship is destroyed by meteoroids. In an alternate version of events, he works at the same television studio but his assistant drowns instead. The assistant’s widow is Anna, whom he recognizes. Another storyline has Nemo and Elise married with three children. However, their marriage is unhappy as Elise suffers from borderline personality disorder and chronic depression. She has attacks of hysteria and, despite Nemo’s attempts to save their marriage, ultimately leaves him to pursue Stefano.
Alternatively, after being rejected by Elise, Nemo resolves to marry the first girl who will dance with him at the school prom. That night, he dances with Jean. While taking her home, Nemo pledges to marry her and be successful. Despite being successful and having two children, Nemo is unhappy and bored with his life. Nemo writes over all his possessions to Jean and leaves his family. Now making all of his decisions randomly via coin toss, he goes to the airport, and pretends to be a passenger named Daniel Jones and is taken to a hotel by a waiting chauffeur. At Jones’ hotel room, Nemo is murdered while taking a bath, and his body is dumped in the woods by assassins, confused by contradicting description given to them about Daniel Jones and the man they just murdered.
Running throughout all the many paths his life could take or has taken, the adult Nemo recurringly awakens in a surrealistic world dominated by argyle patterns. This setting seems artificial, like a movie set, and often appears to bleed over into his other lives. Following clues that he finds scattered throughout this city, he ultimately arrives at a crumbling, abandoned wooden-framed house. He stumbles upon a DVD player hooked up to a television screen. In the strangely interactive video, the 118-year-old Nemo converses with the 34-year-old one. He explains that the younger man does not exist. This is a universe where Nemo Nobody was never born, and his consciousness is stuck in some sort of limbo. He states that he is experiencing the story from the end and that he must stay alive until 5:50 AM on 12 February 2092.
Before his death, Mr. Nobody tells the journalist that neither of them exist. They are figments in the mind of the 9-year-old Nemo at the train station, as he was forced to make an impossible choice. The young boy tries to find the correct decision, following each choice to its conclusion. Eventually, the boy takes a third option: to not make the choice at all. He leaves both parents and runs away towards an unknown future. This ambiguous choice somehow leads to him and Anna reuniting happily. The film returns to old Nemo on his death bed. The calculated time arrives and Mr. Nobody’s last words are watched by the world. The expansion of the universe comes to a halt and time appears to reverse. The universe ceases to dissipate, and finally begins contracting. Consequently, Nemo’s life simplifies itself. He is able to return to his childhood, watch his parents get back together and be with Anna. The 118-year-old man cackles triumphantly as he springs back into awareness with the realization that his younger self has finally found his one true love and life.