Fiction penned by an incomer (5)
I believe the answer is:
alien
'incomer' is the definition.
(person living in an area they didn't grow up in)
'fiction penned by an' is the wordplay.
'fiction' becomes 'lie' (I've seen this in other clues).
'penned by' is an insertion indicator.
'lie' put within 'an' is 'ALIEN'.
(Other definitions for alien that I've seen before include "Offensive" , "immigrant" , "Little green man, perhaps" , "exciting film based in space" , "coming from overseas" .)