Unscrupulous US city travellers heading north (6)
I believe the answer is:
amoral
'unscrupulous' is the definition.
(I've seen this in another clue)
'us city travellers heading north' is the wordplay.
'us city' becomes 'LA' (Los Angeles).
'travellers' becomes 'Roma' (Romani people).
'heading north' is a reversal indicator (in a down clue, letters go up).
'la'+'roma'='laroma'
'laroma' back-to-front is 'AMORAL'.
(Other definitions for amoral that I've seen before include "unconcerned about ethics" , "Having no code of ethics" , "Without ethics" , "Unconcerned with correctness" , "without guiding principles" .)