Angry young man briefly accompanied returning book (7)
I believe the answer is:
rebecca
'accompanied returning book' is the definition.
'rebecca' can be an answer for 'book' (I've seen this before). I am not sure about the 'accompanied returning' bit.
'angry young man briefly' is the wordplay.
'angry young' becomes 'rebec' (I am not sure about this - if you are sure you should believe this answer much more).
'man' becomes 'cal'.
'briefly' means to remove the last letter.
'cal' with its last letter taken away is 'ca'.
'rebec'+'ca'='REBECCA'
(Other definitions for rebecca that I've seen before include "Mrs de Winter (novel by D. Du Maurier)" , "Biblical wife of Isaac and mother of Jacob and Esau" , "The first Mrs de Winter (Du Maurier)" , "Daphne du Maurier book; girl's name" , "Du Maurier heroine at Manderley" .)