Spoilers
“Tunguska”

The X-Files is back to using the black oil in some horrifying manner. The mysteries of what the black oil is and what the government knows about it is the driving force behind this story.
Alex Krycek returned to cause trouble for Mulder and Scully. Mulder winds up in a Russian gulag and Scully winds up before Congress, being threatened with contempt of Congress if she does not reveal Mulder’s whereabouts.

Mulder and Scully get their hands on a rock that contains the black oil, to the chagrin of Cigarette Smoking Man.
There were some fun scenes in this episode including a handcuffed Krycek dumping a thug from Skinner’s apartment balcony. The thug, a courier for CSM, fell to his death. This show provided some real strength to the character of Krycek as he really outmaneuvered Mulder.

That final scene with the black oil dropping onto a confined Mulder, creeping beneath his face to cover his eyes in blackness was devastating.
This was a part one, and it was a tough one to stop on, but I did not have time to continue the part two before Smackdown.