Cho Soo-ji – Starring Lee Si-young

Homicide detective with attractive looks. Soo-ji was picked to join the Olympic team as rifle shooter but unexpectedly got pregnant during that period and was dropped by the team. She joined the police force and worked her way up to becoming a detective. Then one day, her daughter Yoo-na was killed. Her daughter was attacked and killed when Soo-ji was chasing a convict on a stakeout. While grieving over her loss, the murderer who caused her daughter’s death was found innocent by the court because the killer’s family was very powerful. It was a shocking court decision. Before her daughter died, she clearly identified her assailant despite her broken bones. She vowed to bring her daughter’s killer to justice and plans how to avenge her death with the help of a mysterious person who calls himself the “guardian.”

Jang Do-han – Starring Kim Young-kwang

A prosecutor at the Seoul Supreme Prosecutor’s Office. He skipped high school and got his GED, after which he took the bar exam (no law school degree required) and passed it to become the youngest person to ever join the bar. His father was framed for being a North Korean spy and was subsequently tortured by South Korean prosecutors. To get revenge, he joined the prosecutor’s office and pretended to be an eager-to-please prosecutor to get close to senior prosecutor Yoon Seung-ro, who is a corrupted prosecutor that finds loopholes to act with impunity in his powerful position. To ensnare Seung-ro, Do-han came up with the idea to create the “Guardians.” But then he encountered Soo-ji in his line of work and her indomitable personality jeopardizes his plans.

Kim Eun-joong – Starring Kim Tae-hoon

A prosecutor at the Seoul Supreme Prosecutor’s Office. It was love at first sight when he met Soo-ji. Then one day, Soo-ji’s daughter is killed in a horrible incident. Although Eun-joong handled the case, Do-han and Seung-ro sabotaged it so that he could not carry out a proper investigation to uncover the truth. His failure to prosecute the killer led to events where Soo-ji became a fugitive. With the purpose of uncovering Seung-ro and Do-han’s improper conduct, Eun-joong joined the special task force in charge of capturing the Guardian.

Seo Bo-mi – Starring Kim Seul-ki

She holed herself in her room where she monitors hacked security cameras installed across the nation. Her family was murdered when she was 17 and she was the sole survivor. After her tragic loss, she became a Guardians member. She has monitors covering all the walls of her room where she watches hacked live security footage of criminals carrying out their acts of crime. While volunteering for the Guardians group, she recovers her self-esteem and comes to terms with her loss.

Gong Gyung-soo – Starring Kim Ki-beom (Key of SHINee)

A skilled computer hacker. When he gets a mission from the Guardians leader, he will hack the mobile phone of his target and retrieve personal information or hack into ministry computer servers to obtain case files. His mother went missing when he was little and that led to the breakdown of his family. Gyung-soo was in and out of juvenile detention centers and penitentiaries as he moved from place to place as a loner. Then he joined the Guardians group because he believed it would help him find his missing mother.