Yagami Light is an intelligent young adult who resents crime and corruption in the world. His life undergoes a drastic change when he discovers the Death Note, a notebook that contains five written instructions:
There are many other rules that are revealed as the story develops, usually in the form of sequence breaks in between scenes. After several experiments with the Death Note, Light realises the notebook's authenticity and encounters the previous owner, a shinigami called Ryuk. Light explains his plans of becoming a god with Ryuk. Soon, the number of inexplicable deaths of criminals catches the attention of the International Police Organization and the a world famous detective, "L". L quickly learns that the serial killer, publicly known as "Kira" (キラー, derived from the Japanese pronunciation of the word "killer"), is located in Japan and can kill people without laying a finger on them. Light realizes that L will be his greatest nemesis, and begins a cat and mouse game with L.
- The human whose name is written in this note will die.
- This note will not take effect unless the writer has the subject's face in their mind when writing his/her name. Therefore, people sharing the same name will not be affected.
- If the cause of death is written within 40 seconds of writing the subject's name, it will happen.
- If the cause of death is not specified, the subject will simply die of a heart attack.
- After writing the cause of death, the details of the death should be written in the next 6 minutes and 40 seconds.
Light attempts to create an alibi by helping L and his investigate team track down Kira. His plan is impeded by a second Kira, famous model Amane Misa, and her shinigami Rem. Misa and Light meet and work together; they are increasingly suspected by L. To save themselves from execution, Misa and Light temporarily relinquish control of their Death Notes—erasing their memories of the shinigami and the notebooks—and are placed under constant surveillance by L.
During their detention, a third Kira under the employ of the Yotsuba Group appears. Light and Misa are freed when it becomes apparent that they are not responsible for the murders of Yotsuba's rivals. The investigative team infiltrate Yotsuba and discover the third Kira is Yotsuba member Kyosuke Higuchi and attempt to capture him. Upon Higuchi's capture, Light regains the Death Note "just as [he] planned" and kills Higuchi. He completes his complex plan by tricking Rem into killing L. Light becomes the "new L" upon L's death, and continues a charade of searching for Kira.
The narrative continues four years later, with Kira attracting a large network of contacts and a swell of public support. Two children, Near and Mello, raised by L's former guardian Watari to follow L's legacy, serve as antagonists to Light: Near as an independent detective; and Mello as a member of the Mafia. Mello's first action to oppose Kira is to kidnap the director of the NPA, and after his murder, Light's sister Sayu, to use as a bargaining chip to obtain the Death Note. Light's Task Force recapture Sayu and learn Mello's real name after Light's father Soichiro trades half of his remaining life for the ability to discover anyone's names, but Soichiro later dies of gunshot wounds.
Concurrently, Near and several members of the Task Force begin to suspect Light of being Kira. In response, Light persuades Misa to give up her Death Note and raises another Kira, Teru Mikami, a prosecutor and fervent supporter of Kira. Mikami kills Kira's former spokesman for being greedy and recruits Kiyomi Takada, a newscaster and Light's former girlfriend, to replace him. Mello returns and kidnaps Kiyomi, who manages to kill Mello with a hidden Death Note piece. Light then makes Takada commit suicide to prevent her from implicating him, but Mikami, unaware of Light's actions, attempts to kill her with his own Death Note. Near reveals that Mikami's notebook is a fake, and is therefore able to prove Light is Kira. Realising Light has lost, Ryuk uses his own Death Note to kill Light with a heart attack.