Genial fellow in a story (7)
I believe the answer is:
affable
'genial' is the definition.
(synonyms)
'fellow in a story' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'in' is an insertion indicator.
'story' becomes 'fable' (fable is a kind of story).
'a'+'fable'='afable'
'f' going inside 'afable' is 'AFFABLE'.
(Other definitions for affable that I've seen before include "Pleasant and friendly in manner" , "having easy manners" , "nice" , "Pleasant to talk to" , "Polite and friendly" .)