This first book in a well-received series that has produced five volumes as of February 2014 contains five occult mysteries solved by a group of college students.
Shinji Yagami is a freshman at Setsuetsu University and belongs to the Occult Interest Group (OIG) on campus. He sees ghosts and spirits, but he'd prefer to have nothing to do with them, and his only reason for signing up is that Koyomi, the beautiful girl he's had a one-sided crush on since high school, has joined the group. It seems she is especially susceptible to spirit possession.
In the first story, Kabe ni iru kao (The Face on the Wall), the members of the OIG solve a mystery brought to them by a male student, who claims that the face of a woman keeps appearing on the wall of his apartment. He recounts how stain-like marks that look like a face appeared on a wall that was completely clear before. He was so spooked by the event that he changed apartments, only to have the same kind of marks show up on the wall at his new place. He reluctantly decided to move again, but the same thing happened a third time. Wondering what he can do about it, he solicits their help. The five members of the OIG agree to spend the night at his apartment to observe what happens.
They have a late-night snack and share some sake as they wait. Around midnight, the marks forming the face become enlarged. Shinji, who sees spirits, realizes that the problem rests in an antique toy the student has. The former owner of the toy had been raped and impregnated by her stepfather, and ultimately killed the child she bore as well as her stepfather before committing suicide herself. The toy was something she had obtained as a special offering to her child, and now she was appearing as she did because she couldn't stand that her precious toy had been taken away.
In this way, the stories center on paranormal phenomena that haunt students and cause them to seek the help of the OIG. Shinji and the other highly distinctive characters who form the group are at pains to protect Koyomi as they set about solving the mysteries.