Valiant mayor’s novel charity (9,4)
I believe the answer is:
salvation army
'charity' is the definition.
(I know that Salvation Army is a charity)
'valiant mayor's novel' is the wordplay.
'novel' indicates an anagram (letters in a new or novel order).
'valiant'+'mayors'='valiantmayors'
'valiantmayors' anagrammed gives 'SALVATION ARMY'.
(Other definitions for salvation army that I've seen before include "peaceful force" , "Charity" , "Christian body noted for social work and bands" , "The Booths' organisation" , "those helping the homeless at Christmas!" .)