A diplomat's skill occupying criminals - those employed by the spies (8)
I believe the answer is:
contacts
'those employed by the spies' is the definition.
I can't judge whether this defines the answer.
'a diplomat's skill occupying criminals' is the wordplay.
'a diplomat's skill' becomes 'tact' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'occupying' is an insertion indicator.
'criminals' becomes 'cons'.
'tact' put within 'cons' is 'CONTACTS'.
Can you help me to learn more?
(Another definition for contacts that I've seen is " Communicates".)