False adage about spy boss causes harm (6)
I believe the answer is:
damage
'harm' is the definition.
(I know that harm can be written as damage)
'false adage about spy boss' is the wordplay.
'false' indicates anagramming the letters.
'about' is an insertion indicator.
'spy boss' becomes 'M' (M is the head of MI6 in the James Bond series).
'adage' with letters rearranged gives 'daage'.
'daage' enclosing 'm' is 'DAMAGE'.
'causes' acts as a link.
(Other definitions for damage that I've seen before include "Detrimental effect" , "Harm, injury" , "Harm; reparation" , "vandalism?" , "Impair and lower value" .)