Swindlers seeing their leader tucking into flaky croissant (3,7)

'swindlers' is the definition.
(con artist is a kind of swindler)

'their leader tucking into flaky croissant' is the wordplay.
'leader' indicates taking the first letters.
'tucking into' indicates putting letters inside.
'flaky' indicates an anagram (I've seen this in other clues).
The initial letter of 'their' is 't'.
'croissant' anagrammed gives 'conarists'.
't' put inside 'conarists' is 'CON ARTISTS'.

'seeing' acts as a link.