The X-Files: Season 8, Episode 20

8 - 20: Essence (1)

Mulder and Doggett are investigating the death of a doctor who was suspected of experimenting with alien impregnation in an arson attack on a genetics lab. They discovered that Billy Miles who has been changed into an alien replicate, is trying to erase all evidence of the tests. Now, together with Reyes and Krycek, they must protect Scully and her baby.