Season 1

Kwon Do-hun is an affectionate husband and father, but he is always late or absent at every family event because of his overwhelming work. After putting up for ten years, Kang Yu-ra finally loses her temper and invites Do-hun's ruthless supervisor, Chief Oh Cheon-ryeon, to their home.

Even after meeting Chief Oh, Yu-ra can hardly discard her suspicions. Meanwhile, Do-hun prepares an event at a luxury hotel for his wife.

Yu-ra and Chief Oh encounter again at the hotel suite Do-hun booked. Do-hun attends his daughter's school play and meets his friend, Thomas Wolfe.

Do-hun learns the truth while searching for the sniper who injured his colleague during a mission. Wolfe becomes the target of another sniper.

Chief Oh notices the gunshot wound on Wolfe and recalls someone. Yu-ra gets a call and hears a voice she had long forgotten.

Do-hun is troubled after getting unexpected information about Chief Oh. Yu-ra comes face-to-face with the mysterious caller.

Jo Tae-gu knows about Yu-ra's past, and his subtle threats make her anxious. Do-hun and Chief Oh try to read each other while hiding their true intentions.

Tae-gu consents to leave Korea on one condition. Do-hun finds a picture while tracking down Chief Oh and gets assigned to a sniping mission.

The NIS senior/director calls Do-hun and asks if he found the sniper that killed Butterfly and where that bullet hit her. Director expresses his suspicions about Chief Oh being involved in Butterfly’s murder, while at the NIS headquarters, Ma Young-ji tells Chief Oh about Butterfly’s situation and mentions Do-hun was the only agent who was there when Butterfly was killed. It turns out Chief Oh didn’t know Do-hun was the one sent to kill Butterfly.

The childhood history of Yu-ra and Tae-gu.

The story when Do-hun first met Yu-ra.

An intruder breaking into Chief Oh’s house while she’s asleep. Fortunately, she hears the intruder approaching to attack her and wakes up just in time to fight them off. She overpowers the attacker and shoots him. Just then, Ma Young-ji calls to inform her that there’s something wrong at the NIS headquarters.