Drama had fine pace and a decent balance between present and the past. However it only speed up both in plot and thrill from ep10 upward. Between boring and unlikable main leads and bland supporting ones, villains Im Hying Rak and Do Young Gul were the shining stars of "Undercover". One dissapointment for me was Go Yoon Jo, she seemed promising at first but in the end she wasn't that important and her love triangle was unnecessary. Plot twists in later episodes were surprising and kind of sad but well played, even though with all that tention being build from the first episode, ending seemed anticlimactic and unsatisfying. Music wasn't bad but awfully overused. If the main theme wasn't played several times in an episode, it would be better.