Seven Mysteries.

Tsuyuki looking for club activities to join, goes to the club room of the occult research department, which he accidentally sees. He was forcibly taken there by the director Kato, who he met, and there was the seven mysteries of high school? Is associated with elucidating. Fujii, who is sympathetic to Tsuyuki, joins the group for some reason, and the three of them solve the mystery one after another, but Kato has a big secret that cannot be told to anyone.