Kusanagi and Kishitani visit Yukawa’s physics lab on the university campus. Before Kusanagi can mention it, Yukawa deduces that he is working on the murder on the Old Edogawa River. Kishitani is impressed by Yukawa’s deductive reasoning and explains the particulars of the case. Kusanagi claims that he just wanted to visit his friend, but everyone knows that he really wants Yukawa’s analytical insights. Kusanagi believes that Yasuko is guilty, even though he cannot break her alibi; he explains that Yasuko still had the movie tickets in her purse. Yukawa remarks that if her alibi is real, that is unsurprising. However, if, as Kusanagi suspects, she kept the tickets specifically to establish an alibi, this detail hints at a level of forethought that he finds concerning.

As Kusanagi prepares to leave, he mentions in passing that Yasuko’s neighbor was an alum of their university. Yukawa recalls that Ishigami was a classmate in the math department when he was in the physics department. He calls the mathematics teacher “Ishigami the Buddha” (69) and labels him a genius of the kind that only appears once every century or so. Yukawa is shocked to learn that Ishigami is now working as a mere high school teacher, as Ishigami cared about nothing but math and had always been logical, single-minded, and impossible to read.