Stimulate one new spy, say (6)
I believe the answer is:
incite
'stimulate' is the definition.
(inciting is a kind of stimulating)
'one new spy say' is the wordplay.
'one new' becomes 'in' (I've seen this in other clues).
'spy say' becomes 'cite' (I can't explain this - if you can you should believe this answer much more).
'in'+'cite'='INCITE'
Can you help me to learn more?
(Other definitions for incite that I've seen before include "Goad" , "Arouse to action" , "Encourage (to violence)" , "Egg on" , "Stir up (eg, violence)" .)