Fix where setter admits to espionage (7)
I believe the answer is:
implant
'fix' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for implant that I've seen before include "Insert within a body" , "Inculcate; embed" , "material (medical)" , "Fix securely and deeply" , "Introduce" .)