Setter's intention to return to city once associated with vice (5)
I believe the answer is:
miami
'city once associated with vice' is the definition.
I can't judge whether this definition defines the answer.
'setter's intention to return' is the wordplay.
'setter's' becomes 'im' (referring to the person who set the crossword).
'intention' becomes 'aim' (synonyms).
'to return' says the letters should be written backwards.
'im'+'aim'='imaim'
'imaim' reversed gives 'MIAMI'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for miami that I've seen before include "Floridian city" , "I put out of action when returning" , "Prejudice in favour of one person or thing" , "Resort city in SE Florida" , "tourist centre" .)