“Big Mouth” Lee Jong-suk and Im Yoon-ah started their revenge against Kim Joo-hun.
Park Yoon-gap (Jung Jae-sung) appeared at the place where Park Chang-ho was waiting. Park Chang-ho wondered, “You’re Big Mouse?” Park Yoon-gap said, “Think carefully. If it’s not me, it can’t be explained.” He drew attention by explaining strange things that had happened so far, such as giving cyanide to those who died in the restaurant but deceiving that it was tranquilizer.
However, Park Chang-ho did not believe that Park Yoon-gap was Big Mouse until the end. Park Yoon-gap asked “Tell me about Seo Jae-yong’s thesis. What’s the decisive evidence?” and even showed the tattoo on his wrist. But when Park Yoon-gap did not recognize the meaning of the tarot cards, Park Chang-ho said “You’re not Big Mouse” and left.
Meanwhile, the psychopath prisoner (Yoo Tae-ju) began to react abnormally as if he was on drugs. When he failed to steal nutrients from prisoners in the same room because he could not stand his trembling hands, he immediately turned violent, causing shock. In addition, the three V.I.P members sounded Hyun Joo-hee (Ok Ja-yeon) out to prevent the dismissal of the director. As Hyun Joo-hee treated them unkindly, Jung Chae-bong (Kim Jung-hyun) was delighted that she did not know about the Gucheon Prison’s nutritional supplements.
Ko Mi-ho (Im Yoon-ah) applied to become a full-time nurse at Gucheon Prison. When Ko Mi-ho met Park Mi-young (Kim Sun-hwa) at the interview location, she said “We can’t work with each other”, suddenly giving a war of nerves. At that time, a psychopath prisoner fainted on the ground in the yard after showing withdrawal symptoms and was attacked by an electronic shock gun during the disturbance. Ko Mi-ho saved him by performing CPR. Park Yoon-gap bowed and thanked Ko Mi-ho then asked her to go to work starting the next day.
Ko Mi-ho immediately secretly collected blood from the hospitalized prisoners and handed it to a mysterious person. Park Chang-ho gave Choi Do-ha (Kim Joo-hun) a transcript containing information revealing that Park Yoon-gap was the right arm of Big Mouse. It was only until he returned to the prison that he got to know about Ko Mi-ho getting a job at the prison. “Get her out of here”, Park Chang-ho angrily shouted at Park Yoon-gap, but Park Yoon-gap did not give in and suggested exchanging the information one by one.
Park Yoon-gap said, “A person Big Mouse trusted got involved in Seo Jae-young’s thesis and died”, telling the reason why he was into Seo Jae-young’s thesis. “Blood was taken from prisoners for a blood test”, Park Chang-ho drew attention as he revealed the content of the thesis. Later, Park Chang-ho tried to persuade Ko Mi-ho, but she boldly responded, “What are you going to do to get the blood from the prisoners here? I’ll do it. You can do other dangerous things for me.”
Choi Jung-rak (Jang Hyuk-jin), who came to arrest Park Yoon-gap according to Park Chang-ho’s plan, rushed into the prison. Park Chang-ho said he would publish the transcript of his conversation with Park Yoon-gap and suggested using the corruption to conduct an arrest investigation on Park Yoon-gap. It was then revealed that the person who recorded the conversation was Gan Su-cheol (Kim Dong-won). Choi Jung-rak made Park Yoon-gap frustrated by adding the fact that Choi Do-ha tried to replace his director position with Gan Su-cheol.
The fact that Hyun Joo-hee caused a car accident while being drunk on something was broadcast. Seeing this, Park Chang-ho said to Ko Mi-ho, “I think we caught two with our plan. Big Mouse and Mayor Choi Do-ha”, and showed a delightful expression. In fact, Park Chang-ho knew that Choi Do-ha was the hidden accomplice in Seo Jae-young murder case, not Gong Ji-hoon (Yang Kyung-won). Park Chang-ho and Ko Mi-ho already expected that they would catch both Big Mouse and Choi Do-ha, given that Big Mouse would soon appear in front of Park Chang-ho after he started attacking Mayor Choi.