During the Kan'ya Festival, Satoshi participates in a quiz contest with the intention of advertising Hyoka. Satoshi makes it to the final four and runs into an acquaintance, Tani, from the Go Club, who tells him some Go stones were stolen. Meanwhile, various clubs report that various small things have been stolen from them as well, and that at each crime scene, there is a note left by the culprit, known only as "Jumonji".