Jeremy Frost is a young man who hasn't had dreams in years since his abusive father hit his head with a baseball bat. A doctor specializing in dreams prescribes him African Dream Root tea to bring back his dreams in order for him to find a bit of relaxation during the night. Jeremy indeed has vivid dreams, but also experiences that with the dream root he has the power to enter other people's dreams and control them.
He enters the sleeping mind of his doctor, and keeps him locked up in his nightmares until death. When Bobby Singer investigates the case, Jeremy enters Bobby's dreams and confronts him with his dead wife. Sam and Dean come to help Bobby, but when Dean accepts a beer from Jeremy (a mistake Bobby did before), he too becomes a possible victim of Jeremy's.
When Jeremy confronts Sam inside Dean's dream, Sam takes control of the dream and conjures Jeremy's father (possibly with the help of his psychic powers).