Ishigami walks to school following his usual route. He notices the usual homeless people along the way. To his surprise, Yukawa appears asking to speak with him. While discussing the aforementioned homeless people, whose daily routine Ishigami previously referred to as “clockwork,” Yukawa tells Ishigami that even though people are like cogs in a clock, “the world needs its cogs; and even a cog may say how it gets used.” This is an implicit rebuke to Ishigami, who has reduced human life, specifically that of the hopeless people, to something mechanistic and insignificant. We find out later that among these homeless people, there is one person who ends up being used by Ishigami to make his plan work. Yukawa’s words are therefore a coded way of informing Ishigami that certain of Ishigami’s misdeeds, which are to be revealed later, have been discovered. Ishigami replies ironically that Yukawa is using up the time that they have allotted for their conversation.

Yukawa also shares his opinion about the police investigation, telling Ishigami that the police don’t have evidence to incriminate Ishigami. He further shares his opinion that the police are following a dead end and going in the wrong direction, comparing their mistake to that of a student who mistakes an algebra problem for a geometry problem, which is how Ishigami described the mistakes made by his students. Yukawa goes further in describing the case as one of “camouflage,” one where the substance of the case has been covered up and sidetracked by irrelevant distractions. The police have been so obsessed with the matter of Yasuku’s alibi, that they have overlooked the key to solving the case, which is that Ishigami has committed a separate murder to draw attention away from the real murder.

In support of this “camouflage” hypothesis, Yukawa points out several aspects of the case that raise suspicion: the matter of the victims’ clothes not being fully burned (despite it being a simple matter to completely burn the clothes) and that of the stolen bike (i.e. the one stolen by victim before going to the site where the body washed up) being completely new. By pointing out how these details don’t add up, Yukawa is communicating to Ishigami the fact that he has solved the case.

It’s for this reason that Yukawa is able to answer for Ishigami the question of “which was more difficult, formulating an unsolvable problem, or solving that problem.” Yukawa has solved the problem that Ishigami has formulated, which is to cover up Yusaku’s murder by murdering a person unrelated to the case so that date of death would be March 10, the date for which Yusaku has an alibi and didn’t commit any crime, as opposed to March 9, the date that Yusaku actually murdered Togashi.

Yukawa’s motive for talking with Ishigami is purely out of concern based on their mutual friendship. There is no need to question the sincerity of Yukawa here. Just as Ishigami’s humanity is betrayed in his soft spot for Yusaku, so Yukawa’s humanity is betrayed by his care and concern for Ishigami. What Yusaku represents for Ishigami, Ishigami represents for Yukawa. They both have a sentimental side belied by their high-level discussions of physics and mathematics.

The chapter then shifts to a restaurant, where Kudo has taken Yusaku and Misato out on a date. Kudo shares with Yusaku a threatening note that he received in his mailbox. The note tells him to stay away from Yusaku. In addition, Kudo shares photograph secretly taken of him from a time when he met with Yusaku on a previous date. All of his points to Ishigami being a stalker who can’t accept Kudo being involved with Yusaku. The reader is left doubting whether or not Ishigami is really a virtuous protector or a possessive and insecure manipulator. Eventually, we’ll discover that the pretense of being a stalker was all premeditated in order to enable Ishigami to make a confession of guilt and thereby save Yusaku.

Misato, who has been uncomfortable the whole time of this date, expresses dissatisfaction with the possibility that Yasuku might end up marrying Kudo, considering it a betrayal of Ishigami. Her presence here helps to underscore the conflicting emotions felt by Yusaku, who wishes for a normal married life with Kudo despite feeling gratitude to Ishigami for all his sacrifice.

When Misato and Yasku return home, Ishigami calls, informing her about three envelopes and a memo left in her mailbox. How these are to be used are explained in the letter, and Ishigami tells Yusaku that this will be his last phone call. It is at this point that we shift to Kusanagi, who receives word that Ishigami has turned himself in