Ah... the infamous "3." It's like one of those cheap late night thriller/horror movies, except it doesn't contain any nudity. If this were any venue other than broadcast television, there'd be breasts and a lot more blood everywhere.
Everything is dark and has a erotic/killer undertone to it with Mulder attracted to the vampire, Kristen, who is running from a trio of vampires with cheesy names like "The Son," "The Father", and "The Unholy Ghost" and trying to fight her base impulses as a vampire. In the end, they all die. The details in between aren't important or relevant, but there are random Bible verses and proclamations about eternal life--all glossed over for the weird vibes going on between Mulder and Kristen.
The entire episode made me squirm and now I even feel uncomfortable writing and rewatching parts of the episode. Yet again, The X-Files misses the mark on a traditional creature.