This is an EXCELLENT episode!
Mulder and Scully investigate the deaths of a hiking couple. The place they were found is a well known spot of UFO sightings, thus they search for a theory around abduction killings. But... is it really aliens who did it?
There turn out to be slight inconsistencies with other abduction records.
From that point on, the story involves rapidly into one direction, only to switch into some completely different theory. Answers which have been found aren't answers anymore, solutions to the riddle are discarded quickly and even Mulder is clueless about the odd killings. What does "reality" mean...?