City firm really concealing books (8)
I believe the answer is:
coventry
'city' is the definition.
(I know that Coventry is a city)
'firm really concealing books' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'really' becomes 'very' (I've seen this before).
'concealing' is an insertion indicator.
'books' becomes 'NT' (New Testament).
'very' going around 'nt' is 'ventry'.
'co'+'ventry'='COVENTRY'
(Other definitions for coventry that I've seen before include "English city" , "Send to this city to ostracise" , "Place" , "cathedral city" , "West Midlands city" .)