117-year-old Nemo Nobody is ill and facing his last days as he looks back on his past and a particular crucial moment -- at the age of nine, Nemo's parents divorced, and as his mother and father stood on a train platform, he had to choose who he would go with, and whether he would live in the United States or Great Britain. Either choice would bring with it a wide variety of possibilities regarding the sort of life he would lead, and Nemo imagines nearly all of them. But as Nemo considers the many different paths his life could have taken, his memory begins to fail him, and he finds it increasingly difficult to be certain which was his real life and which is a product of his imagination.

Nemo Nobody est le dernier mortel de l'humanité. À 118 ans, en 2092, il est une attraction pour les journalistes qui veulent tout connaître de sa vie. A-t-il choisi de partir au Canada avec sa mère ou de rester en Angleterre avec son père, lors de leur divorce? Laquelle de ses trois compagnes de classe a-t-il choisie pour bâtir sa vie d'adulte? La belle Anna, la dépressive Elise ou la délicate Jean? Au crépuscule de sa vie, Mr. Nobody n'a plus de certitudes, sinon que ses souvenirs peuvent très bien lui mentir. Et cela lui importe bien peu.