"Biburia Koshodou no Jiken Techou" volume 2 by Mikami En. The subtitle this time is "Shioriko-san and her mysterious days", and there was more focus on Shioriko and her past. It's like a reverse detective story where we learn more about the detective than the various cases. Other than the character development bits, the usual trivia about old books is still there and still great to read.
Previous (2013-01-24): "Biburia Koshodou no Jiken Techou" by Mikami En
Next (2013-02-11): "Puella Magi Madoka Magica, The Novel" by Hajime Ninomae