Was Mia Vallens killing her patients?
That was the big question on Supernatural Season 13 Episode 4 when it became apparent that her patients were all turning up dead, and the brothers tried to find a motive.
The brothers are forced to confront some drama of their own when the murders had links to their worst fears.
Being in the supernatural business for so long, you would think they would be accustomed to all forms of evil.
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Paul Dailly is a staff writer for TV Fanatic. Follow him on Twitter.