Chaeyeon and Minju are the top secret agents of a high class undercover agency named IZ*SK. IZ*SK is an underground facility of the South Korean government which handles conflicts against North Korea in shadows. Everything the government can't handle, they do it themselves without the constriction of the law.  Chaeyeon is the captain of IZ*SK's top team named IZ*ONE. Her girlfriend, Minju, is the team's vice captain. One night, they had to split into two teams. One lovely night turned