They have the right LOVE at the wrong time.

The Undercover Agent falls inlove during his task.

He's task is to watch over the witnessed [Accomplice] daughter and catch the Bomb Lord in South Korea.

HINT :

Xiumin is a spy who falls in love with Seohyun his class mate during his task .

Which he didin't know that she is also hiding something from him. Seohyun was taking good care of Yuri .

 Luhan was also a spy but not in the good side he was assigned to kill Seohyun .

He knew about her real identity but he can't do his task because he had his own REASONS as he grew to develop weird feelings for her.