Conclusion of book messenger (5)
I believe the answer is:
envoy
'messenger' is the definition.
(I've seen this in another clue)
'conclusion of book' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is present in the answer.
The remaining letters 'envy' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for envoy that I've seen before include "Legate" , "Emissary" , "One sent on a mission" , "final words in writing" , "Diplomat" .)