I am using the edition from 講談社・こうだんしゃ, 1999. The pagination I give in my reading notes refers to this edition. 

This is the fourth book of the Kaga series (if you look on Amazon, you will see that it is the third book, but the publisher announces it as the fourth. But it does not really matter anyway). The title is very appealing because it seems that there are only two suspects and that the whole investigation will be to determinate which of the two did it. This supposition is confirmed by the wrap-around band which says: “容疑者は二人”・ようぎしゃはふたり which means “two suspects”.

So, no classical investigation where you have a bunch of suspects to be slowly narrowed down through facts collecting, interrogation and deduction.

I always make a list of the characters every time I read a Japanese novel. The first reason is that I have great difficulties to remember Japanese names. The second reason is that I often forget how to pronounce the names when I see them only in kanji, and that is frustrating. The third reason is that characters are sometimes called by their family names, sometimes by their first names, depending on who calls them, and I can’t figure out who is who.

Characters

In order of appearance (not of the character in the story, but of the first time the name is mentioned – which is the only time the name is given with furigana)

• 和泉園子・いずみそのこ・Izumi Sonoko She is working in the sales department of an electronic components manufacturer in Tokyo. She lost both her parents and doesn’t see her brother much, but they often keep in touch.
• 佃潤一・つくだじゅんいち・Tsukuda Junichi Graduate. Trying to make a living through painting but slowly giving up his dream. When he meets Sonoko, he is selling his paintings, knowing that he will have to give up his artistic ambition to find a job.
• 井出係張・いで（がかりちょう）・Ide  Sonoko’s chef
• 弓場佳世子・ゆばかよこ・Yuba Kayoko  Sonoko’s best friend. They met in high school but became close friends at university. She wanted to work in the mass media but ended up working in an insurance company.
• 和泉康政・いずみやすまさ・Izumi Yasumasa  Sonoko’s brother. Living in Nagoya. He is a police officer, works in the traffic section. I think we can say that he is a “traffic officer.”
• 山辺刑事・ やまべけいじ・ Detective Yamabe.
• 加賀恭一郎・かがきょういちろう Kaga Kyoichiro. His grade is serjeant: 巡査部長・じゅんさぶちょう. I don’t know much about police grades, I just looked at the Wikipedia page on police rank. He is often called 加賀刑事・かがけいじ, Detective Kaga.
• 本間・ほんま・Honma Section chief in the traffic police
• 田坂・たさか ・Tasaka colleague from Yasumasa. They were in the same school year at the police academy.
• 坂口・さかぐち・Sakaguchi junior colleague from Yasumasa
• 吉岡オサム・よしおかおさむ・Yoshioka Osamu. Architect working in the same building than Sonoko
• フジワライサオ Fujiwara Isao. Manager of the design company where Tsukuda Junichi is helping.
• オガタヒロシ  Ogata Hiroshi Student working in the design company.
• 相馬・？？ This is the false name Yasumasa uses when calling Tsukuda Junichi. There are different ways to pronounce it, and I have no idea how it should be pronounced here.
• 佐藤幸宏・さとうゆきひろ Sato Yukihiro Friend of Junichi who works in an Italian restaurant and lives in the same building.
• オカベシンイチ・ Okabe Shinichi. Had a car accident.
• 野口・のぐち Noguchi, a friend of Yasumasa, works at the forensics.
• 山岡・やまおか Yamaoka, chief of Sonoko’s section.
• 笹本明世・ささもとあきよ Sasamoto Akiyo, Sonoko’s colleague.
• 藤岡聡子・ふじおかさとこ Fujioka Satoko. She was in the same university than Sonoko.