Be honest and firm with spy about end to espionage (4,5)
I believe the answer is:
come clean
'firm with spy about end to espionage' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'be honest' is the wordplay.
'be' becomes 'come' (coming is a kind of being).
'honest' becomes 'clean' (I've seen this before).
'come'+'clean'='COME CLEAN'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for come clean that I've seen before include "Be completely honest" , "Divulge" , "Confess fully or arrive after ablutions" , "Informally, confess fully - arrive washed?" , "Tell all" .)