Crazy mystics holding key that affects the whole network (8)
I believe the answer is:
systemic
'crazy mystics holding key that affects the' is the definition.
Both the answer and definition are adjectives. Maybe there's a link between them I don't understand?
'whole network' is the wordplay.
'whole' becomes 'system' (I have seen 'Complex whole' mean 'system' so perhaps 'whole' could also mean 'system').
'network' becomes 'ic' (I can't explain this - if you can you should give a lot more credence to this answer).
'system'+'ic'='SYSTEMIC'
Can you help me to learn more?
(Other definitions for systemic that I've seen before include "Affecting a body, institution, etc as a whole" , "Relating to a complex whole" , "insecticide" , "My sect is concerned with affecting the whole body" , "Relating to the whole organism" .)