Diary of a Prosecutor

Sun Woong, a prosecutor at the Jinyeong Branch in the southernmost of Korea introduces his workplace. The case he's working on now is a dispute between a shaman and his customer. They believe he didn't perform exorcism after being paid, but the shaman himself disagrees. He's performed in at least 21 times. As the investigation carries on, Sun Woong does recognize the shaman's abilities. But something doesn't seem right.

Sun Woong is surprised to see Myung Ju, an old acquaintance he's known since in college years. She's pretty, smart, and one of the most competent prosecutors in Korea. Everyone at the Jinyeong Branch start to wonder what must've caused her to come all the way down to this countryside.

Jung Woo gets to work with Myung Ju. On his first day in Myung Ju's office, an old lady wearing shabby clothes comes to the office. He falls for the old lady's act, and that's when Myung Ju shows up to set things right. Meanwhile, Jong Hak is heavily stressed out from work and pressured by his colleagues and supervisor, and he ends up falling ill and being taken to the hospital.

A middle-aged man named Kim Young Choon is arrested after he assaulted his boss in the middle of the night. He is also known to have committed the obstruction of business against his boss. Two charges are filed against Kim Young Choon. Sun Woong and Myung Ju are asked to work together to dig in the cases and reach an agreement on the punishment for Kim Young Choon's doing.

Criminal Department 2 comes across an unexpected tip about a hidden gambling den in the mountains. They decide to send someone to the gambling den undercover, but the only person whose face is unfamiliar to the target is Myung Ju. However, she does not know a thing about gambling. Sun Woong and the team must turn Myung Ju into a gambler overnight.

The crackdown on the hidden gambling den is a success and hordes of people are arrested and interrogated by the prosecutors of Jinyeong. Among the people who were brought in from the gambling site is a man who seems to know Myung Ju quite well. Myung Ju decides that she must excuse herself from the case, but her next case is also one that reminds her of a hurtful past.

Sun Woong gets a surprise visit from his son Jae Hoon. It turns out that Jae Hoon is in trouble for bullying a classmate. Meanwhile, Myung Ju works on a school violence case in which a middle-school girl jumped from her school building after being bullied. Sun Woong deals with uncomfortable conversations at work and is unsure of what he should do about his son.

Yoon Jin has a tough few days trying to juggle work and her sick twins. With her mother-in-law and husband to consider on top of it all, she passes out from exhaustion and wakes up in the emergency room. Sun Woong and the others go home after her family arrives, but the next morning, Yoon Jin is nowhere to be found.

Promotion season is officially here, and the prosecutors of the Jinyeong Branch are being extra cautious not to stir things up. However, Jung Woo breaks the peace, making Min Ho anxious. To make things worse, the notorious Mr. Hwang, also known as the Ax, is back to torment the prosecutors of Jinyeong.

Branch Chief Kim In Ju is on the brink of his big promotion to Chief Prosecutor when he comes across the biggest crisis of his career. Meanwhile, Myung Ju and Sun Woong continue to bicker over everything, including a fraud case that involves a local assemblyman and his son. Many people in positions of power try to hinder the investigation.

As Branch Chief Kim In Ju prepares for his retirement, the people of Jinyeong Branch get busy preparing for a big farewell. Chief Kim wonders what he will do after he retires and meets other former prosecutors who are now working elsewhere. He also remembers a certain shameful incident from many years ago. Meanwhile, Jong Hak deals with a very annoying video influencer.

Choi Jong Hoon, the new branch chief, arrives at the Jinyeong Branch and he a harsher boss than anyone could have possibly imagined. He seems determined to grill Criminal Department 2, despite Min Ho's efforts to get on his good side. Meanwhile, Jung Woo gets asked out on a date by Mi Ran while also receiving unwanted favoritism from the new branch chief.

In a nation that boasts two fraud cases every minute, all sorts of swindlers and their victims show up at Jinyeong Branch. Meanwhile, a familiar face reappears in a trial that Sun Woong attends, requesting to be released on bail. As Mi Ran struggles to overcome the trauma of Jung Woo's rejection both offline and online, Jung Woo takes on his first solo case.

Sun Woong's negligence brings shame and dishonor on Branch Chief Choi Jong Hoon and apparently the entire Prosecution. The battle between Sun Woong and Chief Choi begins with both their pride on the line. As Min Ho continues to take the flack for Sun Woong's insubordination, the 2K Motors trial gets handed over to Myung Ju right before Sun Woong demands a sentence.

Inspectors from the Supreme Prosecutors' Office come to Jinyeong and a dangerous game of Russian Roulette begins. The inspection team seems determined to dig up every error made by the Jinyeong prosecutors in both their work and personal lives. Meanwhile, Jung Woo sees the downtrodden team atmosphere as an opportunity and comes up with a plan for a secret date with Mi Ran.

The former branch chief of Jinyeong, Mr. Kim In Ju, makes a brilliant comeback as the head of the special investigation team. Mr. Kim requests to have either Sun Woong or Myung Ju join his team in Seoul and they make a bet to decide who gets to go. To settle the bet, the pair take a trip to find the original owner of Sun Woong's accidental carpenter's ruler.