3. I Saw The Devil (2010)
They say revenge is a dish best served cold, but it came with an overly generous helping of chills in the Korean horror-thriller I Saw The Devil.
The story follows a special agent who is hellbent on avenging the murder of his pregnant wife at the hands of a serial killer, and the results are harrowing.
I Saw The Devil plants the viewer directly into the mind of a monster as the protagonist succumbs to the dark urges his partner's grisly death have awakened.
It's a slow-burner, but when the fear kicks in, it never lets up.
One minute you're rooting for the stricken hero, the next you're fighting to keep your lunch down in light of his latest atrocity and wrestling with a troubling thought - could abject trauma push you over the edge this way?