The story of Day One focuses on the life of Ulises Albet (Álex González). he is a computer prodigy. He leaves Barcelona and the technological world behind after the suicide of his sister, a victim of bullying. Ten years later, a mysterious call from his former partner and best friend, Samuel Barrera, forces him to return in the middle of the Mobile World Congress. He warns him that the world is in danger. This fact forces the protagonist to confront his past and the progress of technology.