Accompanying dog into party about books (10)
I believe the answer is:
concurrent
'accompanying' is the definition.
(thesaurus)
'dog into party about books' is the wordplay.
'dog' becomes 'cur' (cur is a kind of dog).
'into' is an insertion indicator.
'party' becomes 'con' (abbreviation for Conservatives).
'about books' becomes 'rent' (I can't justify this - if you can you should give a lot more credence to this answer).
'con'+'rent'='conrent'
'cur' inserted inside 'conrent' is 'CONCURRENT'.
(Other definitions for concurrent that I've seen before include "Working together" , "Cooperating with" , "acting together" .)