The air in Amiens (4)
I believe the answer is:
mien
'the air' is the definition.
(I've seen this in another clue)
'in amiens' is the wordplay.
'in' indicates the answer is hidden within the clue.
'MIEN' is hidden within 'amiens'.
(Other definitions for mien that I've seen before include "Appearance, bearing" , "Counterance - mine?" , "Appearance is strangely mine" , "aspect" , "A manner like mine" .)