On this episode of Supernatural…

Sam and Dean discover that a parasite is taking over people and turning them into homicidal maniacs thirsting for blood.

They head to a military base, where they discover Cole is also checking on his friend, Kit.

The three team-up to try and find Kit, but Cole ditches Sam and Dean to check on his friend.

The parasite gets inside Cole, and Dean agrees to help him sweat it out rather than kill him.

Sam tries to save Kit, but is forced to kill him.

The parasite does leave Cole, after a few fights with Dean.

Sam is shaken up by not being able to save kit.

Cole thanks Sam and Dean, and he heads back to his family.