"If I don't have to do it, I won't. If I do have to do it, make it quick," is the basic principle by which energy conservationist Houtarou Oreki lives. But after his sister convinces him to join the Classics Club, Houtarou's life is turned upside down when he meets Chitanda, a perpetually-inquisitive girl who challenges the boy's easygoing existence. Intrigued by the slightest hint of a mystery afoot, Chitanda doesn't hesitate to pester the reluctant yet highly analytical Houtarou into satisfying her curiosity at every turn, no matter how small the problem. Alongside fellow members Satoshi and Ibara, the group tackles cases ranging from a self-locking classroom door, a strangely-popular library book, and even the shadowy history of the very club to which they belong!