Ragtime composition for Simenon's detective (7)
I believe the answer is:
maigret
'simenon's detective' is the definition.
(I've seen this in another clue)
'ragtime composition' is the wordplay.
'composition' is an anagram indicator (letters arranged or composed in a different order).
'ragtime' anagrammed gives 'MAIGRET'.
'for' acts as a link.
(Other definitions for maigret that I've seen before include "Policeman" , "cracker?" , "Simenon''s detective-superintendent" , "Simenon's Inspector" , "Fictional detective" .)