“Kush” is episode five of season one of Sanctuary.
This episode opens with a flashback to Victorian times, and Dr. Magnus is with John Druitt in a carriage as he proposes to her. Then she comes around in a crashed plane in the snowy wasteland of the Hindu Kush.
Magnus and Will had been on a trip with Silvio to recover a creature when it escaped from its cage and killed the co-pilot – who was currently flying the plane – and caused it to crash. They were flying to a facility in New Delhi – it seems the Sanctuary is a rather vast world-spanning organisation with huge resources, even more than would be guessed from the facility seen to date.
Now, they, and five other survivors, are trapped by a storm in an inhospitable place, where it’s difficult to rescue them from, although Ashley and Bigfoot do set out to help, but help is many hours away. Magnus and Will start having visions, Will of his mother and Magnus of Druitt; visions that are incredibly realistic.
When the first person dies, it seems to be suicide. When the second does, it’s obviously murder. They are trapped in the plane, and presumably with the creature they captured. It’s impersonating one of them, but they don’t know who, and sending visions to cloud their minds.
Trapped in a snowy wasteland with some sort of creature killing them off, and disguising itself as one of them? Very John Carpenter‘s The Thing in plot.