Outside work agent becomes mawkish (5)
I believe the answer is:
soppy
'mawkish' is the definition.
(thesaurus)
'outside work agent' is the wordplay.
'outside' indicates putting letters inside.
'work' becomes 'op' (abbreviation for opus).
'agent' becomes 'spy' (spy is a kind of agent).
'op' put within 'spy' is 'SOPPY'.
'becomes' acts as a link.
(Other definitions for soppy that I've seen before include "Overly sentimental" , "Daft" , "Mushy" , "Feeble; sentimental" , "Mawkish" .)