Dead rousing session putting up beacon - rake ash now and then (6)
I believe the answer is:
'dead rousing session' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for seance that I've seen before include "Sitting - can see (anag)" , "Dead-contacting session" , "Meeting in which medium attempts to contact the dead" , "Meeting held by a medium" , "Medium experience?" .)