Favouring denouement in which Morse loses case (9)
I believe the answer is:
endorsing
'favouring' is the definition.
(favour can mean to endorse or promote)
'denouement in which morse loses case' is the wordplay.
'denouement' becomes 'ending' (a denouement is the end of a story).
'in which' means one lot of letters goes inside another.
'loses case' means to look at the middle letters (the case is the outside letters).
The middle letters of 'morse' are 'ors'.
'ending' placed around 'ors' is 'ENDORSING'.
(Another definition for endorsing that I've seen is " backing".)