Brief extract from impressive unfinished book (7)
I believe the answer is:
epitome
'brief extract' is the definition.
(epitome can mean a summary)
'impressive unfinished book' is the wordplay.
'impressive' becomes 'epic' (I've seen this before).
'unfinished' means to remove the last letter.
'book' becomes 'tome' (a tome is a book).
'epic' with its last letter taken off is 'epi'.
'epi'+'tome'='EPITOME'
'from' is the link.
(Other definitions for epitome that I've seen before include "Paradigm" , "classic example" , "Archetype, typical example" , "Embodiment or perfect example" , "Summary of a written work" .)