Hotaro Oreki joins the Classic Lit Club at his high school at the behest of his sister to keep it from being shut down; his best friend, Satoshi Fukube, and Eru Chitanda, a curious girl who enjoys mysteries, also join the club.

Eru grows bored with the club's lack of activities, and suggests that they prepare an anthology for the school's fall culture festival. While locating previous anthologies, the club discovers a mystery in the library.

Eru talks to Oreki about why she joined the club and asks for his help with something personal; still unable to find any anthologies, the club members run into an obstacle when trying to search the club's previous room.

Eru seeks help from Satoshi and Mayaka in trying to work out what happened to her uncle. The club members meet up at the Chitanda estate to present their research and share their theories.

Hotaro finds himself torn between his grey life and the rosy life others live. Hotaro gets a call from his sister leading him to believe his theory regarding the events of Sekitani's expulsion may have some holes.

The sound of an outburst from Eru's math class interrupts Hotaro's history class, leading to a discussion in the Classic Lit Club about the seven deadly sins and what may have angered Eru.