"Tempus Fugit/Max" is probably the best, most pristine example of the X-Files mythology episodes. Unlike most of the other mythology episodes (especially the pilot), it manages to hang the mythology elements on an physical, forensic and answerable mystery—What happened to the plane?—and letting the mythology elements—abductions, MUFON weirdos, sinister government operatives, crashed ufos, recovered alien technology, incredulous locals—interact in and around it. That the key mystery is intricate enough to support the episode without the mythology is essential. If you took the military's cover story at face value, it would make complex enough premise for a Law and Order episode. The actual work of collecting and analyzing the evidence provides suspense which is eventually released, instead of cascading into an increasingly sprawling web of never-answered sub-mysteries, something no individual player can really keep straight.