Tale of heroic deeds in the picture book (4)
I believe the answer is:
epic
'tale of heroic deeds' is the definition.
(I've seen this before)
'in the picture book' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EPIC' is hidden in the letters of 'the picture book'.
(Other definitions for epic that I've seen before include "blockbuster" , "great film" , "Impressively great" , "Larger than life" , "Long adventure story" .)