A Shinigami (Death God) drops a notebook in the human world where a young genius picks it up. The notebook displays the message: "The human whose name is written in this note shall die" It is the notebook of death that can determine when a person will die. Light Yagami, an extremely bright elite university student, is the one to possess this ultimate tool that should remain only in the hands of God. Light decides to create an ideal world and begins to hold the scales to judge the criminals in his discretion.

Meanwhile, the ICPO (International Criminal Police Organization) has placed a mysterious detective called "L" in the Japanese police force to investigate the series of criminal cases. "L" is an eccentric genius who has successfully solved many cases in the past that were deemed unsolvable. With L's expertise, the police are able to tighten the investigative screws over these cases, but Light, also cleverly manipulating the notebook of death, tosses and shakes the investigation. The future of mankind is at the mercy of this fierce battle between the two brains.