Informant? I dispute that with raging fire! (8)
I believe the answer is:
'informant?' is the definition.
'i dispute that with raging fire' is the wordplay.
'i dispute' becomes 'noti' (I can't justify this - if you can you should give a lot more credence to this answer).
'that with' is a charade indicator (letters next to each other).
'raging' indicates anagramming the letters.
'fire' with letters rearranged gives 'fier'.
Can you help me to learn more?