..where we are in for a surprise. True to his word, Ishigawa goes to Bententei to buy a lunch bento. Yasuko is there, of course, and is very worried about his rare visitor last night. After enough furtive conversation and sideways glances to awake suspicion in a corpse she she finds out it was just an old classmate from his university days. After the morning rush Yasuko has a break with the Yonegawas, the owners of the shop. The detectives have visited them, and they're very relieved that Togashi didn't come to the store and didn't contact Yasuko (ahem).
The afternoon sees the entrance of Kudō, our possible plot twist, into the store and the story. A regular customer of Yasuko's at the first place she worked, he followed her to the next one (where both, by the way, met Sayoko, the bento shop owner's wife who also worked there). Yasuko and Kudō are not lovers, though not for his lack of trying. He even got into a fistfight with Togashi once as he escorted Yasuko home after work (I'm not altogether sure I would blame Togashi too much for that). He can apparently spend a large chunk of money and time every week for years with a hostess instead of his wife and son, without either of them protesting. Different strokes, I guess. Anyway, they reacquaint themselves, and go to a nearby place for coffee and a chat.
It rains as they leave, and he offers to drive her directly home. As they pull up by the building they are met by Ishigawa, who is uncharacteristically short-spoken and withdrawn on the phone with Yasuko later that day. At that point a light finally goes on for Yasuko. She realizes that Ishigawa may have the hots for her, and that may be the reason he helps her concealing a murder.
Now, I may not be the most socially or psychologically insightful person in the world ("computer science degree", 'nuff said) but this stretches the rubberband of believability to its breaking point. You'd expect a neighbor to lend a hand with a couch. You'd not expect them to lend a hand with a murdered ex-husbands corpse. Furthermore, Yasuko is a former hostess, a job whose single most important qualification (well ahead of being young and beautiful) is the ability to read and understand the moods, the desires and the motivations of other people. Sayoko, the bento-shop wife told Yasuko outright that Ishigawa is in love with her. And still it supposedly takes her weeks - and a third of the book - to figure out that there just might be something more behind Ishigami's willingness to help her conceal a murder than wanting to be a good neighbor. Yes, it is a murder mystery and you're supposed to check your skepticism at the door, but come on now; nobody is this dense.