Episode 10 of Big Mouth opens up with a twist in the tale as the person who comes to meet Chang-ho in the church is none other than the warden himself! The warden admits to being Big Mouse. When Chang-ho shows him a tarot card, the warden tells him to speak directly. Chang-ho doubts his identity. When the warden shows him a tattoo of Big Mouse’s symbol on his arm, Chang-ho says that the owner wouldn’t wear a leash. The warden is just one of Big Mouse’s dogs. Chang-ho leaves the church and pulls a recorder out from his pocket, having captured the whole conversation.
Mi-ho goes to visit Jerry, he isn’t initially in his bed but soon comes there. Mi-ho says Chang-ho was mistaken in thinking Jerry had met Big Mouse. Jerry agrees to testify at Chang-ho’s trial.
In a movie theatre, Mayor Choi watches the documentary about Gucheon. He stops at the photograph of a family and we get a flashback featuring the same young boy from the picture. A car is burning and the small boy is crying out for his grandfather but is held back by others. Gong Ji-hoon arrives and points out that the young boy looks a lot like Mayor Choi. But he had it checked and apparently the boy died soon after. Mayor Choi and Ji-hoon exchange words, each claiming to one-up the other. Then, Mayor Choi gets a call from Chang-ho, who wants him to be a witness to his interrogation by the prosecution the next day. The mayor agrees.
In the prison, the inmate on death row is shivering and having problems with his vision. Desperate for the supplements given by the nurses, he gets into a fight with the other inmates in his cell. In the cafeteria, the room leader and Chairman Yang talk about how everyone is fighting over the medicines.
At Gucheon University Hospital, the head nurse speaks to Han Jae-ho and tells him to change the medicine since it seems to be having side effects. The other two VIPs arrive and they dismiss her concerns. The three of them then come face to face with Hyun Joo-hee. She claims they will be fired soon while they are confident the Elder will protect them since they killed a man for him.
On the way to his interrogation, Chang-ho is warned by the warden to not do anything stupid.
Later, the warden looks at nurse resumes for the prison, including Mi-ho’s.
Joo-hee goes to her office in the hospital to find Jung Chae-bong waiting for her. He asks her to help them not get fired but she says it’s out of her hands. Outside, the other two VIPs ask if she has any idea that they changed the medicine. Chae-bong says no.
Mi-ho arrives to be interviewed for the nurse position. The head nurse and another nurse from Gucheon University Hospital are also there.
Suddenly, a fight breaks out in the courtyard between the death row inmate and his cellmate. The guards surround him and are forced to stun him with tasers multiple times before he falls down. The alarms bring the nurses out there. Mi-ho starts CPR and manages to save the inmate. The warden is impressed with her.
The mayor arrives at Chang-ho’s interrogation. Chang-ho starts by saying he wants the drug charges dropped. A flashback shows us it was the mayor who got Chang-ho drugged, while in the present he promises to get the charges dropped. Chang-ho then reveals the recording of him and the warden. Since the warden couldn’t read the tarot card correctly, Chang-ho knows he’s not Big Mouse.
Since the warden has been blackmailing and extorting inmates, Chang-ho tells them to use corruption charges to arrest him. When they have enough evidence, he’ll give them the rest of the recording. The mayor agrees. Chang-ho also tells them to cover for him so he can keep looking for Big Mouse inside the prison.
Ji-hoon watches the whole thing and later tells Prosecutor Choi to do as the mayor tells him.
As Chang-ho returns, he notices birds that seem to be dropping dead from the sky. Back at the prison, the warden puts him into solitary confinement.
At a hospital, a doctor tells Mi-ho that the psychopath didn’t test positive for any narcotics. The prison guard who is there with her, tells her that she got the job. The guard, who is a prominent face often seen in a commanding position, gets a call from Choi Do-ha. While he’s away, Mi-ho draws a blood sample from the sleeping inmate. She later hands it to someone else.
At the prison, the room leader is on duty and gives food to Chang-ho. He also tells him that Mi-ho is now working at the prison.
As the warden shows Mi-ho around, the two decide to drop all pretense. Mi-ho knows the warden is Big Mouse’s right-hand man while the warden knows Mi-ho has information about Professor Seo’s paper.
Chang-ho meets with the warden and angrily tells him to let Mi-ho go from the prison. After an argument, they settle on a game of 21 questions. Chang-ho asks why Big Mouse wants to know about Seo Jae-young’s paper. Warden replies it’s because someone that Big Mouse cared about died due to the paper. Warden asks him what is in the paper and Chang-ho replies that it is about the blood taken from the inmates at the prison. He refuses to answer any more questions.
Mi-ho and Chang-ho meet and Chang-ho begs her to leave the job. But she insists that she is the only one who can help him get the inmates’ blood out of the prison.
At that moment, the prosecutor arrives and arrests the warden on charges of blackmail and extortion. He calls Ji-hoon for help but the latter doesn’t seem bothered. As the warden is taken away, Mi-ho and Chang-ho observe the inmates and try to look for anyone looking worried or frustrated.
Later, Chang-ho is called from the cafeteria as the acting warden wants to meet him. He goes to the VIP room to find Mayor Choi seated there. The prison guard from before, Gan Soo-chul, enters. He is now the acting warden. Chang-ho thanks the mayor who says that he still doesn’t fully trust Chang-ho and won’t until he brings in the real Big Mouse.
Meanwhile, at the hospital, Joo-hee packs up her stuff and takes a drink from her desk. She drives and sips on it but soon her vision begins to waver, the way it did with Chang-ho in Episode 1.
The mayor tells Chang-ho that Gan Soo-chul will take care of everything he needs. They then get news about Joo-hee’s accident and the mayor rushes out.
Later, Chang-ho walks Mi-ho out and they talk about killing two birds with one stone — Big Mouse and Mayor Choi. A flashback takes us back to when Mi-ho got the dead patient’s blood analysed at the NFS. Since the mayor was with her at the time, Chang-ho says that if the results are manipulated that means the mayor was involved. Mi-ho gets the results and sees that they are indeed manipulated. She conveys the same to Chang-ho.
Back in the present, they discuss how Big Mouse now seems to be attacking Choi Do-ha. Chang-ho believes that the mayor will retaliate and in the process, they can catch both of them.
Another episode, another twist. This time, we find out that the warden has been on Big Mouse’s team this whole time. As more cards are revealed, things seem to be getting deliciously convoluted and it’s a fun ride to be on.
The next spotlight seems to be on the prison guard, Gan Soo-chul, who is now acting warden. While he wasn’t really a suspicious character before, Soo-chul was definitely present at the more pivotal moments in the show. It’s intriguing to now see him move from background to foreground.
Choi Do-ha continues to be hinted at as the real Big Mouse, which means that as ingenious as Chang-ho and Mi-ho’s plan is, the chances of it going wrong are sky high.
Episode 10 continues to be jam-packed with events that engross the viewer. The stakes are higher than ever and almost every character seems to have something up their sleeve, which is terribly exciting.