Not in step with partners? On the contrary (5)
I believe the answer is:
passe
'not in' is the definition.
(I've seen this in another clue)
'step with partners? on the contrary' is the wordplay.
'step' becomes 'pas' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'partners? on the contrary' becomes 'se' (I can't explain this - if you can you should give a lot more credence to this answer).
'pas'+'se'='PASSE'
Can you help me to learn more?
(Other definitions for passe that I've seen before include "Master key - picture mounting" , "Old hat" , "Out-of-date (French)" , "Old fashioned - in France" , "-- -partout" .)