What Alain-Fournier pens inside story (4)
I believe the answer is:
info
'inside story' is the definition.
(I've seen this in another clue)
'what alain-fournier pens' is the wordplay.
'pens' says the answer is hidden in the clue (pen can mean to contain or cage).
'INFO' is hidden within 'what alain fournier'.
(Other definitions for info that I've seen before include "Knowledge (colloq.)" , "Gen (colloq.)" , "News" , "Latest" , "Dope" .)