"Energy conservationist" Hotaro Oreki joins the Classic Lit Club at his high school at his sister's behest, to keep it from being shut down. Also joining the club are his best friend, Satoshi Fukube, and Eru Chitanda, a curious girl who enjoys mysteries.

Hotaro is enlisted by Eru to appear in a Dolls' Festival parade that her local shrine holds every year. When construction work unexpectedly causes a last-minute detour, it leaves the participants wondering what went awry.