In Tokyo's Shitamachi area, there is a second-hand bookstore called "Tokyo Bandwagon ~ Shitamachi's Extended Family Tales". It is well known around the neighborhood, and has been the Hotta's family business for 4 generations. Kanichi, who is currently managing the bookstore, is the patriarch of the family. His son, Ganato, is a legendary rocker of his time. Ganato's second son, Ao, is the only one born of a different mother amongst his siblings. Ao is an ex-delinquent but is actually a very kind-hearted young man.

"The riddle of the disappearing encyclopedia", "The child left behind and the book that could open holes", "The torn painting and the break in of the book archives"; All the unbelievable incidents that happen at Shitamachi are somehow resolved by this somewhat eccentric family.