a undercover agent as a singer, protects a family that is in danger. Donghae finds that someone is after his friend Yoochun and his little sister. Chung-Ae an assassinator works for a gang to protect her brother. During a mission Chung-Ae not knowing that Yoochun would be there, accidenly attacks her  brother and Donghae.  Donghae telling yoochun that hes an under cover cop looking for the gang that Chung-ae is working for. Chung-ae has to find a way to get rid of Donghae without Yoochun, Donghae or anyone else finding out her secret. But each time her chances slip and her feelings grow, Donghae finds out what Chung-ae does for a living and is willing to turn her in. but before he can he realizes that all there lives are in danger and his love for Chung-ae is stopping him.........