The X-Files: Season 4, Episode 8

4 - 8: Tunguska (1)

Mulder receives information about a militant group that is collecting material to make a highly explosive weapon. An assault team breaks up the group and, during the raid, Mulder and Scully find Alex Krychek, who supplied Mulder covertly with the information on the group. With the traitor's help, the agents are able to obtain a diplomatic pouch containing a rock pulled from the ground in the Tunguska region of Russia.