Girl's story taking in idiot (6)
I believe the answer is:
lassie
'girl's' is the definition.
(lassie is a kind of girl)
'story taking in idiot' is the wordplay.
'story' becomes 'lie' (I've seen this before).
'taking in' indicates putting letters inside.
'idiot' becomes 'ass' (I've seen this before).
'lie' enclosing 'ass' is 'LASSIE'.
(Other definitions for lassie that I've seen before include "Girl from Scotland and dog from film" , "Canine film star" , "Young Scottish girl or Hollywood lost dog" , "TV/film dog" , "Film and TV dog" .)