The Immortal (2000)

Season 1: Episode 8

Blaylock, a demon who can change forms and favors plagues, breaks into a government research lab and steals a virulent new germ-warfare disease. He escapes ahead of Raphael, who is taken into custody by the FBI. He manages to convince the agent to free him and then help him track down the supposed terrorist. Meanwhile, Goodwin and Sara have taken the plane that the disguised demon is supposed to be on. It goes down in the woods near a reservoir, and they quickly find out that everyone on the plane are demons! Raphael arrives and manages to stop the demon just before he can dump the vial in the reservoir. The demons takes his form, but is no match for the Immortal's sword skills.