Prediction

Prediction (予測, Yosoku) is the 8th chapter of Volume nine and 78th chapter overall.

Plot
Near, through process of elimination based on what he has seen the notebook do, figures out that the fake rule is the "If you don’t write a name in the Death Note after 13 days, you die" rule.

He calls L and tells him that he had Mello in custody but he escaped. Light is furious that Near might have gotten the chance to question Mello first and also suspects that Near let him go deliberately. However, Near swears that he escaped by his own means and begins to ask L about the existence of Shinigamis and their ties to the Death Note. Light doesn’t deny it and tells him that he didn’t divulge those details because he thought Near would never believe him.

Near asks him if he knows about a fake rule in the Death Note. Light is forced to admit that through process of elimination, it is only logical that the "13 day" rule is the fake one. However, Light suggests that Mello may have been lying and asks Ryuk if all of the rules are true. Ryuk answers that they are.

This confirms to Near that the Shinigami, the Death Note, L and the Task Force are all together and he asks if any of them ever knew the late L personally. Light panics and hangs up. Near takes this as an affirmative answer.

Light warns the other members of the team that Near probably suspects one of them of being Kira. This turns them against Near. Light calls Near back and admits that they did know the late L. Near then asks why, after killing L, Kira did not kill the rest of them as well. Telling them that he believes Mello over a Shinigami, he insists that the "13 day" rule is a fake and that Kira is among them and making the Shinigami lie.

Light counters this by suggesting that Kira got hold of L's details through other means, but Near's observations cause the planting of seeds of doubt in the Task Force. In a conversation aside, Aizawa in particular points out that Light was cleared of being Kira by being held in custody for over 50 days without access to the Death Note (see chapters 35 "Whiteout" and chapters 35 "Father and Son"). If the "13 day" rule is a fake then that means that Light can again be considered a suspect.

Near then suggests testing the rule himself by writing Mello’s name on the Death Note, bluffing that even if he dies after 13 days it will help progress the investigation. Light consults with the Task Force: Matsuda is willing to go along in order to get justice for Soichiro Yagami who was killed by Mello, but the others object to using the Death Note at all. Light passes this decision on to Near.

Light now knows that Near suspects him of being Kira and that the whole conversation was an act so that he could get the investigation team to have doubts about him. He tells the team that because Near is fishing for information then Mello can’t be too far behind since he happens to have Mogi's cell phone number. Just then, Mogi’s phone rings and Mello is on the other line.

Conception
Ohba said that the chapter's title "Prediction" relates to the predictions made by Light and Near in the chapter. Light predicted that Mello would try to contact one of the task force members, and then Near predicted that the 13-day rule is fake and also that the original task force members have met the original L.

Ohba explained that he made many of the predictions correct so that it would make the plot move forward a lot more. Ohba believed that the story would in fact not "work as well" if the predictions tuned out to be wrong.