Diary of a Prosecutor tells the stories of overworked prosecutors' daily lives in Seoul.

Lee Sun Woong works as a prosecutor in the district office in Jinyoung. He seems relaxed and doesn't appear to have a desire to succeed. Meanwhile, Cha Myung Joo is an elite prosecutor on the fast track in the Central District Prosecutor's Office in Seoul. One day, she is suddenly transferred to the district public prosecutor's office in Jinyoung.