I was rather skeptical before watching a movie from 2013 (my experience with older korean dramas has been so-so) and the title sounds cheesy as well(at least in english language). Fortunately, I was proven wrong.

This is a great thriller in vein of "The Call" and "Forgotten". Expect dark and gory scenes, complex psychology and lotsa plot twists. I think too many actually; the final plot twist was really not needed and came out of nowhere. This didn't really spoil the "journey" of getting there, but the ending could have been better.

There are also several plot holes, mostly related to FLs past and behaviors.
The acting also could have been better, while the performance of main characters was very good(especially Uhm Ki Joon, he's so different from his roles in later dramas here!), the side characters were overacted.

For these reasons, I can't rate this drama more than 8/10 overall. Which is still a very good rating and I recommend it.