• Jung Ryeo-won as Noh Chak-hee, an ace lawyer with the highest winning rate in a big law firm, Jangsan, who becomes a public defender.
• Lee Kyu-hyung as Jwa Si-baek, a public defender often referred to as crazy and eccentric.
• Jung Jin-young as Jang Ki-do, CEO of Jangsan Law Firm.
• Kim Hye-eun as Oh Ha-ran, wife of Jang Ki-do.
• Lee Sang-hee as Yoo Gyeong-jin, a detective at the Metropolitan Crime Investigation Unit.
• Kim Sang-ho as Shin Chi-sik, owner of Mokgol Dumplings.
• Park So-jin as Jang Yi-yeon, daughter of Jang Ki-do.
• Hong Seo-joon as Oh Dae-hyeon, a strategist who helps and supports Jang Ki-do's ambitions.
• Ko Kyu-pil as Do Young-soo, a clerk at the office of a public lawyer.

No Chak-Hee (Jung Ryeo-Won) works for a big law firm. She is willing to take any risk to win a case and has become an ace attorney at the law firm. She is set to receive a promotion to a partner position, but a problem occurs on a case she accepted. Due to this, she almost gets suspended for a year. Instead, No Chak-Hee begins to work as a public defender. She hopes to return to her position at the law firm where she worked previously. As a public defender, she shares an office with fellow public defenderJwa Si-Baek (Lee Kyu-Hyung).

Jwa Si-Baek graduated from the Judicial Research and Training Institute as the top student. He had his choice of becoming a judge, prosecutor, or attorney at a big law firm, but he chose to work as a public defender. He is enthusiastic with his work and also has a mysterious part of his personal life that nobody knows about.

No Chak-Hee and Jwa Si-Baek don't get along very well, but they get involved in a serial murder case. The victims are wealthy elderly people.