"Furuhonya Tantei no Jikenbo" (Casebook of Old Bookstore Detective) by Kida Junichirou. This book felt very long, partly because it was 4 books combined, but mostly because the writing style was not very focused. It takes a bit of patience to read through each story, but it may be well worth it for the dramatic endings. In mystery terms, the "evidence gathering" phase were rather dull, but the "solution" phase that follows were all very rewarding.
This book might be better illustrated using two lines from the first story:
"Well well, wait a bit. All explanation up to now was just muscle on the side. What you would call subroutines in computers."
"For a computer, you are quite slow in reaching conclusions."
These two lines were the turning point in a very intricate solution. The protagonist has just identified the thief before these lines, which would have been a good place to end the story. But he then continues on to name the other thief, and explains how the same book was stolen twice. The "computer" here is a reference to an 1980 era machine running CP/M that appeared 25 pages ago. Meanwhile, his client correctly observed how slow paced the narration is going. Most of this book felt very much like this segment: subtle references to data that were scattered far apart, wry humor in dialogues that might be deleted without affecting the solution much. Besides these fluff, it's quality mystery that are unlike the usual find-the-murderer fare.
I had expected stories with more content related to the "old bookstore" part of the title, and it's a bit disappointing that the text did not focus on old books more. But for readers with a bit of perseverance, this book is a collection of fine mystery fictions.
Previous (2013-10-31): "Codex Seraphinianus" by Luigi Serafini
Next (2013-11-11): "Hikaru ga Chikyuu ni Ita Koro" volume 8 by Nomura Mizuki