A lawyer with a 10 percent winning rate loses his own case and is conned out of his life savings. Hearing the news, his wife files for divorce, but he is called into a case involving big shots that could save his career.

Changho wakes up in hospital, and is charged with drug abuse and locked up in Gucheon Prison. There is word that a genius con artist who robbed NR Forum has been caught around the same time as Changho's incarceration.

Changho tries to get to the bottom of how he became known as Big Mouse. Miho transfers to Gucheon University Hospital to try to clear Changho's name, and finds something suspicious happening in the cancer ward.

Gong Jihoon decides to test whether Changho is the real Big Mouse as doubts of his identity grow. Miho asks Choi Doha for help with one of Changho's cases.

Changho cross-examines a witness who has important information about Big Mouse. Jihoon approaches Miho to ask for help in finding Seo Jaeyoung's thesis.

Miho joins the prison medical volunteer program to meet Changho, but she doesn't recognise the Changho who is getting special treatment in the prison. Miho receives a call about the location of Seo Jaeyoung's thesis.