At the request of his older sister, Houtarou Oreki goes to join the Classic Literature Club upon entering high school to stop it from being disbanded. Upon arriving there, he meets another member, Eru Chitanda, who becomes curious as to how she got locked in the clubroom. After Houtarou’s habit of thinking things through to the end helps him solve the mystery, Houtarou’s classmate, Satoshi Fukube, also decides to join the club. The next day, the club investigates a mystery involving a recruitment poster for a secret club. As they leave that day, Houtarou reveals to Satoshi that he made the mystery up as it would’ve been too much effort to solve another mystery they had been discussing had Eru caught wind of it.