The exploits of FBI Special Agents Fox Mulder and Dana Scully who investigate X-Files: marginalized, unsolved cases involving paranormal phenomena. Mulder believes in the existence of aliens and the paranormal while Scully, a skeptic, is assigned to make scientific analyses of Mulder's discoveries that debunk Mulder's work and thus return him to mainstream cases.
Mulder and Scully, reunited at last, head for an active volcano under a geological study and find a deadly life form that can survive in the searing heat of the crater and is killing the scientists to avoid being discovered.