Call into a post office and public house with a set of books (9)
I believe the answer is:
apocrypha
'a set of books' is the definition.
(set of books of the Bible)
'call into a post office and public house' is the wordplay.
'call' becomes 'cry' (as in a bird's call).
'into' is an insertion indicator.
'post office' becomes 'po' (abbreviation).
'and' means one lot of letters go next to another.
'public house' becomes 'pha' (I can't explain this - if you can you should believe this answer much more).
'a'+'po'+'pha'='apopha'
'cry' going within 'apopha' is 'APOCRYPHA'.
'with' is the link.
(Other definitions for apocrypha that I've seen before include "In which Judith is" , "text often excluded" , "Set of religious books t" , "Collection of fourteen Old Testament books" , "Doubtfully-authentic writings" .)