Kim Je-Ha (Ji Chang-Wook) is former solider for hire. He is also called K2. He is hired as a bodyguard by Choi Yoo-Jin (Im Yoon-A). Choi Yoo-Jin is the wife of a presidential candidate (Cho Seong-Ha) and the daughter from a chaebol family. Meanwhile, Ko An-Na (Yoona) is the secret daughter of the presidential hopeful. She is also a recluse.

When an unknown toxic gas strikes Seoul in an unprecedented act of terror, Yong-nam has just met Eui-ju from college by chance at his mother's birthday banquet. The city falls under sudden noxious gas attack and together, they must escape the panic-stricken city.