Fiend started to stir and protested publicly (12)
I believe the answer is:
demonstrated
'protested publicly' is the definition.
(as in taking place in a public demonstration)
'fiend started to stir' is the wordplay.
'fiend' becomes 'demon' (synonyms).
'to stir' indicates an anagram.
'started' anagrammed gives 'strated'.
'demon'+'strated'='DEMONSTRATED'
'and' is the link.
(Other definitions for demonstrated that I've seen before include "shown up" , "made public protest" .)