The story unfolds largely through dialog between the four characters as they puzzle over the murder of a friend and argue about which one of them is the murderer. Aside from a few flashbacks, everything takes place in a single room, making for an interesting writing exercise, but as a reader the exercise grows tedious after 200 pages or so, especially since the characters aren't very likeable, even if you can't help but sympathize with them a little. It's best if you read it quickly.
This is a very quick and easy read, written in a simple conversational style, and the Japanese is quite simple.