We have the synopsis for Supernatural season 14 epiosde 8.
 
SUPERNATURAL
“Byzantium” — (8:00-9:00 p.m. ET) (TV-14, LV) (HDTV)
OUT OF THE DARKNESS – When Sam (Jared Padalecki) and Dean (Jensen Ackles) join forces with an unexpected ally, the outcome will alter the course of two lives. Meanwhile, Heaven faces an attack from a dark force, driving Castiel to make an enormous sacrifice to make things right. The episode was directed by Eduardo Sanchez and written by Meredith Glynn (#1408). Original Airdate 12/6/2018.

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Who is the unexpected ally? Whose lives will be altered? What sacrifice will Cas make? Give us your thoughts in the comments or in the discussion thread for episode 8