放課後はミステリーとともに (houkago ha misuterii to tomo ni, After School Comes with a Mystery, 2011) is a series of linked short stories by 東川篤哉 (HIGASHIGAWA Tokuya, born 1968). According to the appreciation which is added at the end of the book (a common feature of bunko format books), the stories were first published in a magazine over several years, starting in 2003. As the title suggests, the stories have a school setting. Apparently they are part of a larger series with the same setting (which might explain some things I didn't understand while reading them).
The school is a Japanese high school and the narrator is 霧ケ峰淳 (KIRIGAMINE Ryou), the vice president of the school's Detection Club. The club is devoted not to detective fiction, but to actual detection; and Ryou has business cards printed with "Kirigamine Ryou, Great Detective" on them. (Great Detective is a recognised profession in the world of Japanese detective stories.) In case it's not already obvious, these are youth oriented, comic mysteries. The youth oriented part means that I don't get some of the comedy, which often runs on stereotypes that I'm not familiar with. It may also be the reason that none of the mysteries actually involve murder. They are not "puzzles of everyday life", the Japanese genre of mysteries without a major crime. Almost all the stories involve a serious crime, often attempted murder; but no-one actually dies. This makes it easier for the comedy too.
The balance of comedy and mystery probably comes down more on the mystery side than the Japanese TV drama series "Trick", which is the other Japanese comedy mystery that I'm familiar with (though I've only seen part of it). The parts of the comedy that I got are generally a very old style of joke, including some things that probably go back to the nineteenth century; but I thought they were pretty well handled. Failed jokes can be almost painful for me; and reading Higashigawa, if I never actually laughed aloud, I never felt that a joke fell completely flat.
The mysteries are also very competently managed, without ever quite reaching the point where you would call them brilliant. All of them involve apparent impossibilities: a thief disappearing from a building whose only exit was watched; a victim pushed from an empty rooftop, which could only be accessed by a staircase where a boy was playing a computer game at the time; a strangling in a field with no footprints but the victim's; and so on.
Despite the "Great Detective" business card, Kirigamine is only rarely the detective, sometimes failing, sometimes not even trying to deduce the culprit, being happy to play Watson to various other characters. One expectation I had reading the stories was that the Detection Club would play some role in the book: it seems pointless to make so much of it in the introduction of the narrator and never use it. In fact, Kirigamine is the only character from the club in the book. Presumably, this should be seen as a spin off to other stories which feature more characters and club activity.
If you're looking for fairly modern, light reading mysteries to practise Japanese with, I imagine these would do very well. Ho-Ling has a lot of posts on Higashikawa, which can give you an idea of his range and point you to other popular books of his. (One warning: if you're thinking of reading this book, you might prefer to read the first mystery in it before reading Ho-Ling's posts on the book.) I certainly expect that I'll try another of his books in due course.