One in the soup in swindle takes flight (7)
I believe the answer is:
crouton
'one in the soup' is the definition.
(I've seen this before)
'swindle takes flight' is the wordplay.
'swindle' becomes 'con' (con is a kind of swindle).
'takes' is an insertion indicator.
'flight' becomes 'rout' (I have seen 'Headlong flight ' mean 'rout' so perhaps 'flight' could also mean 'rout').
'con' placed around 'rout' is 'CROUTON'.
'in' acts as a link.
(Other definitions for crouton that I've seen before include "Fried bread as garnish" , "Small cube of fried bread" , "Small piece of toasted or fried bread served in soup" , "fried food" , "Bit of toast in soup" .)