紀元158年、ローマ帝国はアントニヌス・ピウスの統治下20年目。ローマの浴場設計士ルシウスは還暦を迎えて腰痛持ち、妻のさつきは謎の失踪、息子マリウスは理解不能…。さらに彼を悩ませるのはローマの風呂の仕事であったが!?
20 years after the end of the series, Lucius now 60 years old in the year 158 AD has undergone a midlife crisis and his wife from present day Japan Satsuki disappeared leaving him with his now adult son who never understands him. As he deals with more problems with his life, Lucius once again is transported to modern-day Japan through a bathhouse, leaving him with more adventures that await him.
