People once against spy boss are turned secretly (2,6)
I believe the answer is:
in camera
'secretly' is the definition.
(I've seen this before)
'people once against spy boss are turned' is the wordplay.
'people once' becomes 'inca' (I can't justify this - if you can you should give a lot more credence to this answer).
'against' means one lot of letters go next to another.
'spy boss' becomes 'M' (M is the head of MI6 in the James Bond series).
'turned' says the letters should be written backwards.
'are' back-to-front is 'era'.
'inca'+'m'+'era'='IN CAMERA'
Can you help me to learn more?
(Other definitions for in camera that I've seen before include "(Held) in private" , "secretly" , "Kept private (law)" , "Privately - American (anag)" , "not seen by the public" .)