In the year 158 AD, the Roman Empire is in the 20th year of Antoninus Pius's reign. Lucius, a Roman bath designer, has reached his 60th birthday and suffers from lower back pain; his wife, Satsuki, has mysteriously disappeared; and his son, Marius, is completely incomprehensible... Furthermore, what plagues him most is his work with the Roman baths, but then...!?