In the early Meiji era, against civil unrest and the end of the samurai way of life, Japan's crime rate skyrocketed. As prisons overflow, the government has no choice but to build a new, inescapable prison. This prison is Gokumonjo, located in the center of Lake Biwa, which means it relies on the three sons of the Kumo family to transport criminals to it. But is Gokumonjo truly just a prison for petty criminals?