IRIS

Present day, Hyun Joon is assigned to assassinate a North Korean official. Flashback and Hyun Joon and Sa Woo are hotshot army trainees who meet Seung Hee on different occasions.

Hyun Joon and Sa Woo join NSS and discover their superiors are Seung Hee and Sang Hyun. Their first assignment is a known terrorist, a Japanese man with Syrian citizenship named Yamamoto Takashi.

Hyun Joon and Seung Hee affirm their relationship with a trip to Japan. They are then sent with Sa Woo to Hungary to bring in a North Korean refugee into protective custody.

Now back in the present day, Hyun Joon assassinates a North Korean official, only to have North Korean agents Sun Hwa and Chul Young on his tail. Sa Woo makes the ultimate betrayal.

Hyun Joon becomes a rogue agent and is hunted down separately by Sa Woo, and Chul Young and Sun Hwa.

Although everyone thinks he is dead, Hyun Joon survives thanks to a mysterious benefactor, and escapes to Japan. Sun Hwa follows him with the intent of killing him.

Seung Hee trails Sun Hwa, knowing the latter will lead her to Hyun Joon. The mysterious Vic continues his search for Hyun Joon.

Everyone around Hyun Joon starts to suffer because of the shadowy organization IRIS, of whom NSS director Baek San and Sa Woo are a part of.

Hyun Joon forms an alliance with Chul Young and Sun Hwa, and joins other North Korean agents for a terrorist mission in South Korea.

Sa Woo is the first to realize that Hyun Joon is actually alive. The North Korean terrorists and Hyun Joon infiltrate NSS.

After a close encounter with Seung Hee, the terrorists leave NSS with a detonation device to set up a nuclear bomb. Hyun Joon learns more about his past and the deaths of his parents.

Hyun Joon and Sun Hwa meet his mysterious benefactor and learns more about IRIS. Seung Hee makes her own investigation into the terrorists.

Seung Hee is caught by the North Korean terrorists and brought before Hyun Joon for questioning. Meanwhile, Baek San and Sa Woo take action against the one person who can give answers to Hyun Joon.

A clue brings Hyun Joon to the President of South Korea, whom he informs about IRIS and of Baek San's betrayal. Chul Young struggles between his loyalty to his Director or loyalty to his country.

Time is ticking before the nuclear bomb is detonated within the middle of Seoul, bringing Hyun Joon face to face against Sa Woo.

Hyun Joon and NSS try to bring down Baek San and IRIS as they search for the location of the nuclear bomb.

Finally cleared, Hyun Joon returns to NSS and is formally reunited with Seung Hee. Sa Woo and Baek San are arrested and held by the National Assembly.

Before Hyun Joon and Sun Hwa can retire, Sa Woo and Baek San are freed by IRIS mercenaries, threatening the upcoming North-South Korean summit.

Hyun Joon manages to avenge numerous deaths by eliminating Vic. Sa Woo leads an IRIS operation that takes numerous Koreans hostage in a mall.

IRIS mercenaries appear at the North-South Korean summit, and Hyun Joon manages to take down ringleaders of IRIS.