Tachibana Noboru, a 20-year-old aspiring doctor, lives for tomorrow. Leaving Dewa Province (present day Akita), he turns to an uncle Komaki Genan, who is a town doctor in Edo and gets a job as a doctor of Kodenmacho Prison at Genan’s recommendation. The impressionable Noboru sees the suffering of people who live at the bottom of society as he gets involved in all sorts of incidents inside the prison and solves them with brilliant deductions and jujitsu skills. One night, he is informed that there is an emergency case. A prisoner, Katsuzo, who is due to be exiled to an island for housebreaking, is suffering from a stomachache. Noboru goes to the prison with grim determination. However, Katsuzo feigned his illness in order to lure him to the prison. Noboru is entrusted with a secret task by Katsuzo. It is to obtain his share of 10 ryo from the man who was the ringleader of the housebreaking and hand this money over to a woman called Omitsu in Fukagawa. Omitsu had pledged to be his wife. Sympathising with Katsuzo, Noboru accepts his request.