Hire me to overturn stratagem (6)
I believe the answer is:
employ
'hire' is the definition.
(I know that hire can be written as employ)
'me to overturn stratagem' is the wordplay.
'to overturn' says the letters should be written backwards.
'stratagem' becomes 'ploy' (synonyms).
'me' reversed gives 'em'.
'em'+'ploy'='EMPLOY'
(Other definitions for employ that I've seen before include "Put on the payroll" , "Occupy" , "Put to use" , "Utilize" , "Give work to (person)" .)