TV doctor had one work of fiction (8)
I believe the answer is:
whodunit
'work of fiction' is the definition.
(thesaurus)
'tv doctor had one' is the wordplay.
'tv doctor' becomes 'who' (I've seen this in other clues).
'had' becomes 'd' (I've seen this in other clues).
'one' becomes 'unit' ('unit' can be a synonym of 'one').
'who'+'d'+'unit'='WHODUNIT'
(Other definitions for whodunit that I've seen before include "thriller" , "detective novel" , "Informally, a detective story or play" , "Crime mystery novel, play or film" , "Question commonly posed" .)