Daimon Kaito is a high school student with a passion for puzzles. One day, the student council president hands him a mobile device that guides him to an underground ruin buried beneath the school. Alongside his girlfriend Nonoha, he takes on an "insolvable puzzle" concealed within the ruins, only to discover it is the perilous "The Puzzle of Sage," devised by the clandestine group "POG." Although he succeeds in solving it, this victory marks the start of a puzzle battle against POG.