Dead of Winter

Plot:

When the tunnel world is having an annual event, Paracelcus makes plans to crash the event and do something. When all of the participants arrive, including some friends from the surface, things seem to be OK until Narcisa shows up. It seems she had encountered Paracelcus earlier who had in his possession someone's head who then tried to kill her. They assume Paracelcus is there in disguise. Catherine and Vincent deduce it must be someone from the surface but there are only three whom he knew before he was banished so they try to figure out who could it be.