Connection to a spy (4)
I believe the answer is:
bond
I believe this is a double definition.
'connection' is the first definition.
(bond is a kind of connection)
'a spy' is the second definition.
(James Bond)
'to' is the link.
(Other definitions for bond that I've seen before include "Written promise" , "Link, connection" , "Fastening; secret agent" , "Fictional agent; join" , "Financial asset" .)