One

 "Kira is one person, acting alone."

- Ryuzaki

One (一, Hitotsu) is the fourth chapter of the Death Note series.

Plot
In a hotel room, Soichiro Yagami and the other four remaining members of the Kira Task Force meet the world’s greatest detective, L, who appears as a dishevelled young man wearing casual clothes and who sits in an awkward, hunched way.

They introduce themselves by name only for L to fire an imaginary gun at them! He reminds them that Kira needs to know the name and face of his victim in order to commit murder. How he can kill from a distance is still unknown but the fact that it happens means that they have to be more cautious. L also advices them to avoid taking notes and to address him with a false name.

Matsuda suggests that they could limit the deaths by requesting that the media avoids showing the details of criminals in crime reports. L, however, says that that would be a risky move. When Kira killed Lind L. Tailor, L announced that this had narrowed Kira's whereabouts to the Kanto region of Japan. Kira then started focusing his killings in Japan and the Kanto region in particular as if in a show of defiance. If they stop broadcasting the details of criminals then Kira might start killing innocent people instead on the grounds that they are blocking his attempts to purge the world of crime. L describes Kira as very much like himself: They are both childish and hate to lose!

On the other hand, L suggests that they announce that the USA is now sending 1500 investigators to hunt for Kira in response to the killing of the twelve FBI agents. This will unnerve Kira who will start seeing enemies everywhere, whereas in fact only a handful of men are on his trail.

L now shares his most recent deductions. Shortly after the twelve FBI agents entered Japan, Kira carried out some tests on criminals before killing them. L sent the agents there because he knew that Kira was getting information from the Japanese police and wanted to know the source. Once Kira knew that he was under surveillance, he tested his powers in order to find out if he could manipulate the agent who was watching him. Kira then used this agent in order to obtain a file with the details of all the FBI men, but took the precaution of having it sent to all of them in order to cover his tracks.

Kira usually kills hardened career criminals but in the week preceding the deaths of the agents he killed twenty-three minor crooks or mere suspects. That was probably in order to cover for criminals used and killed while identifying the agents.

In conclusion, they have to find out who was under surveillance during the five days that cover the arrival of the agents in Japan to the tests carried out by Kira; and any links between the agents and the twenty-three crooks killed in the week prior to their deaths.

L admits that showing his face to the others is a victory for Kira since he has never had to do it before. The deaths of the FBI men has also been a major blow. However, he is determined to win the war with Kira. His deductions, the narrowing of the suspects and his determination to win boosts the morale of the other detectives and they get to work with renewed vigour.

L then requests a private meeting with each of them just in order to ensure that none of them are Kira. Most are somewhat shaken by this, but Soichiro insists that they go along with it as a precaution.

L feels that he is making progress. All he needs now is the one clue that will lead him to Kira.

At home, Light Yagami has himself been thinking through the days from when he was first shadowed by Raye Penber. If he left just one clue behind then he is finished.

Meanwhile, Penber's fiancée is convinced that it was no coincidence that he was on the bus hijacked by Kiichiro Osoreda who was subsequently killed when hit by a car. She believes that Kira himself was on the bus and can kill by means other than heart attacks. She makes her way to the headquarters of the Japanese police.

Trivia
This chapter marks the first time that L is seen in person by other characters and shows his habit of sitting hunched up in a chair. In previous illustrations he was alone in a room devoid of furniture &mdash; aside from his computer &mdash; and would stand or sit normally on the floor.

Conception
The title "One" refers to L becoming one of the members of the official Kira Task Force. It also refers to the "one clue" which both L and Light believe could lead to Kira and the fact that a single but very important detail about the case is leading Penber's fiancée to the police headquarters which will be the focus of the next three chapters.