Mastermind born during troubled reign (8)
I believe the answer is:
engineer
'mastermind' is the definition.
(both can mean to contrive or plot something)
'born during troubled reign' is the wordplay.
'born' becomes 'nee' ('nee' is 'born' in French).
'during' means one lot of letters goes inside another.
'troubled' is an anagram indicator.
'reign' with letters rearranged gives 'engir'.
'nee' placed within 'engir' is 'ENGINEER'.
(Other definitions for engineer that I've seen before include "produced" , "Plot" , "Person in charge of building bridges, etc." , "Mechanic" , "Arrange - contrive" .)