Detective Baek Hong Suk (Son Hyun Joo) is A father and a detective, he loses his daughter to a hit and run accident and loses his wife in the shock as well, so he sets out to find out the truth and stands against the center of authority

Special Affairs Team TEN is a criminal investigation unit that tackles the most violent crimes in South Korea. These crimes usually have less than a 10% rate for arrests. They chase the most notorious killers who attempt to commit the perfect crimes.

Yeo Ji-Hoon (Joo Sang-Wook) is former top-notch detective, but now works as a professor. He then becomes the leader of Special Affairs Team TEN. Nam Ye-Ri (Jo An) has been a detective for 4 years. She joins Special Affairs Team TEN because of her psychological reasoning powers. Baek Do-Sik (Kim Sang-Ho) is 24 year veteran detective. He possesses a keen sense of intuition, which he honed from his many years as a detective. Bae Do-Sik also joins Special Affairs Team TEN. Park Min-Ho (Choi Woo-Sik) is a new detective. He joins Special Affairs Team TEN after impressing Professor Yeo Ji-Hoon with his reasoning powers.

Kim Sun Woo, who spent his school days as a troublemaker, decides to make a change in his life and joins the sea special attack team, which is called Poseidon. Sun Woo works as a promising commando, but he unexpectedly becomes entangled in an unsavory incident after 2 years. He is demoted and is sent to a maritime police office in Gunsan city. Sun Woo’s passion cools down and he slowly loses his vision as a maritime policeman. Then one day, Jung Ryul, who has formed a new crime investigation section in Incheon city, visits Sun Woo and asks him to join the team...

Cha Yeon Jin is a high school girl whose outwardly normal existence and reticent character masks her true identity: she is a professional assassin who is seeking vengeance for her mother after watching her killed in front of her eyes. She infiltrates SS1, the secret organization that her mother was connected to, by becoming one of their killers, all the while trying to track down her mother's murderer.

Corrupt detective Han Jong-sik (Kim Seung-woo) takes care of a gang and gets kickbacks to save his daughter. One day he gets news from the organ transplant coordinator that they have found a heart for his daughter (kim Sae-ron). However, he finds out the donor is magician Na Sang-man (Son Byeong-ho) who he put false charges over and was in jail. Sang-man lost his young daughter and wife and became a vegetative state himself. Jong-sik guesses he wouldn’t allow the transplant so he plans a way to get rid of him. Just as Sang-man is about to go over in the hands of a gang and get surgery, he realizes the plan and disappears with Jong-sik’s daughter.

This drama focuses on a group of detectives in the Seoul Gangnam Police Homicide Division who solve crimes based on real life cases with their variety of skills and investigative methods. At the forefront of the team is the impulsive and hotheaded detective Park Se Hyuk and the cold, commanding police chief, Jung Il Do. Park Se Hyuk's passion for his work and rough personality results in a tendency to take action first before thinking later, in contrast with Jung Il Do's by-the-book style.

Set in a tumultuous period where the political scene is murky and various people fought to gain power and the throne, the young king will do anything to strengthen his shaky position in court. His childhood friend Baek Rok leads a secret military force loyal to the king, called the "Black Cloud Swords." Baek Rok lives for his king, his brother Baek Kyul and his lover Jung Yeon, but when his ambitious brother betrays him and leads him into a trap, he finds himself on the run. He becomes a slave and gladiator, eventually returning to Joseon to seek revenge.