The story's only part of the whole picture (4)
I believe the answer is:
epic
'the story's' is the definition.
(I have seen 'Heroic story' mean 'epic' so perhaps 'story' could also mean 'epic')
'only part of the whole picture' is the wordplay.
'only part of' indicates a hidden word.
'EPIC' can be found hidden inside 'whole picture'.
(Other definitions for epic that I've seen before include "On a grand scale, like heroic poem" , "Marathon" , "Heroic, huge" , "Impressive scope" , "Heroic narrative verse" .)