It's just another ordinary day for Houtarou Oreki, who is lounging at home as usual until his sister Tomoe convinces him to work as a lifeguard at the neighborhood swimming pool. Oreki meets the other members of the Classics Club by chance when he arrives to the pool. Eru Chitanda discovers that a white thing that was on a woman's ear a short time earlier has mysteriously vanished, which piques her interest in the mystery. Hyouka: Motsubeki Mono wa follows Oreki and the rest of the Classics Club as they enjoy themselves at the pool while solving the mystery that has piqued Chitanda's interest.