A clan involved in plot must be fair (8)
I believe the answer is:
balanced
'fair' is the definition.
(thesaurus)
'a clan involved in plot' is the wordplay.
'involved' indicates an anagram (involved can mean confusing or complex).
'in' indicates putting letters inside.
'plot' becomes 'bed' (bed is a kind of plot).
'a'+'clan'='aclan'
'aclan' anagrammed gives 'alanc'.
'alanc' placed inside 'bed' is 'BALANCED'.
'must be' acts as a link.
(Other definitions for balanced that I've seen before include "Steady - objective" , "Stable - poised" , "With both sides equal" , "Auntie is supposedly" , "Equipoised" .)