Furious protest before the French murderer returns (10)

I believe the answer is:

demoniacal

'furious' is the definition.
(thesaurus)

'protest before the french murderer returns' is the wordplay.
'protest' becomes 'demo' (I've seen this before).
'before' means one lot of letters go next to another.
'the french' becomes 'la'.
'murderer' becomes 'cain' (Cain who killed Abel).
'returns' is a reversal indicator.
'la'+'cain'='lacain'
'lacain' reversed gives 'niacal'.
'demo'+'niacal'='DEMONIACAL'

(Another definition for demoniacal that I've seen is " Fiendish".)

I've seen this clue in The Independent.

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