Fellow carrying books in cloak (6)
I believe the answer is:
mantle
'cloak' is the definition.
(mantle is a kind of cloak)
'fellow carrying books' is the wordplay.
'fellow' becomes 'male' (fellow is a term for a man).
'carrying' is an insertion indicator.
'books' becomes 'NT' (New Testament).
'male' placed around 'nt' is 'MANTLE'.
'in' is the link.
(Other definitions for mantle that I've seen before include "Gas lamp part; cloak" , "Robe or gas-lamp fitting" , "Loose cloak, shawl" , "Cloak or loose outer garment" , "A cloak, cover" .)