Examine a good book on Tory rival? (10)
I believe the answer is:
contestant
'rival?' is the definition.
(rival is a kind of contestant)
'examine a good book on tory' is the wordplay.
'examine' becomes 'test' (testing is a kind of examining).
'good book' becomes 'NT' (New Testament).
'on' says to put letters next to each other.
'tory' becomes 'con' (abbreviation for conservative).
'test'+'a'+'nt'='testant'
'testant' put after 'con' is 'CONTESTANT'.
(Other definitions for contestant that I've seen before include "Competitor" , "Player" , "Entrant" , "One entering a competition" , "Person vying with others" .)