Mystical gathering (6)
I believe the answer is:
seance
'mystical gathering' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for seance that I've seen before include "Session of spritualists" , "spirited meeting" , "Meeting to contact the spirits of the dead" , "Medium experience?" , "Meeting in which medium attempts to contact the dead" .)