1993-2002, 9 Seasons
Mentioned in Season 1, Episode 8
Two FBI agents investigate unexplainable mysteries in search of the truth (which apparently is out there). Genuinely unmissable event TV during its' 1990's heyday, it was creepy, suspenseful and kept the sexual tension between its two leads crackling way beyond the point any normal humans would have just spontaneously combusted (actually I think that might have been the plot of one episode?).
Both Hywel and Jamie used to love a bit of Mulder and Scully but at some point stopped watching/ lost interest. As did most people. Should probably be held up as proof that even the best shows can outstay their welcome...but then we saw this trailer for the new reboot:
Yes we'll be watching. Even if the films were a bit rubbish.