10 Scariest X-Files Episodes Of All Time

5. Detour - Season 5, Episode 4

The TV spots for Detour posited a very scary question: how can you stop a predator you can't see? That was the basic premise of the episode, which saw Mulder and Scully hunted in the woods by an invisible force. It was quite a unique concept having Mulder and Scully stumble onto a case and then being pursued instead of pursuing and, for the most part, it works.

A big part of the reason why it works is because the invisible (unnamed) creatures are genuinely frightening. One of the most unsettling things about them is their ability to blend into the environment, their faces just being about visible in the bark. There is a sense during the episode that our heroes are in very real danger thanks to this unseen threat.

The episode also has its tender moments, though, and is probably best remembered for the scene in which Scully sings 'Joy to the World' to Mulder while they camp out and try to stave off death.