Curious case comes before 'father of French adventure' (8)
I believe the answer is:
escapade
'adventure' is the definition.
('escapade' can be a synonym of 'adventure')
'curious case comes before father of french' is the wordplay.
'curious' is an anagram indicator.
'comes before' means one lot of letters go next to another.
'father' becomes 'pa' (pa is a kind of father).
'of french' becomes 'de'.
'case' anagrammed gives 'esca'.
'esca'+'pa'+'de'='ESCAPADE'
(Other definitions for escapade that I've seen before include "daring exploit" , "Antic" , "Risky adventure" , "Daring stunt" , "Madcap adventure" .)