Overdue book delighted! (7)
I believe the answer is:
belated
'overdue' is the definition.
(I've seen this before)
'book delighted' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'delighted' becomes 'elated' (I've seen this before).
'b'+'elated'='BELATED'
(Other definitions for belated that I've seen before include "Tardy" , "delayed" , "Out of date" , "Coming too late" , "After the proper time" .)