Councillor is taken in by the devil's sexton (9)
I believe the answer is:
sacristan
'sexton' is the definition.
(I know that sexton can be written as sacristan)
'councillor is taken in by the devil's' is the wordplay.
'councillor' becomes 'cr' (abbreviation).
'taken in by' is an insertion indicator.
'the devil' becomes 'Satan' ('Satan' can be a synonym of 'devil').
'cr'+'is'='cris'
'cris' inserted within 'satan' is 'SACRISTAN'.
(Other definitions for sacristan that I've seen before include "Church officer in charge of sacred vessels etc" , "Church official" , "Church officer in charge of sacred objects" , "Church worker" , "Sexton" .)