Rebel in den, eager, properly prepared (8)
I believe the answer is:
renegade
'rebel' is the definition.
(synonyms)
'den eager properly prepared' is the wordplay.
'properly prepared' is an anagram indicator (I've seen this in other clues).
'den'+'eager'='deneager'
'deneager' with letters rearranged gives 'RENEGADE'.
'in' is the link.
(Other definitions for renegade that I've seen before include "Turncoat, rebel" , "Disloyal - defector" , "Perfidious" , "Apostate" , "Treacherous deserter" .)