Butterfly's innocent officer (5,7)
I believe the answer is:
white admiral
'butterfly's' is the definition.
(white admiral is a kind of butterfly)
'innocent officer' is the wordplay.
'innocent' becomes 'white' (I can't justify this - if you can you should believe this answer much more).
'officer' becomes 'admiral' (admiral is a kind of officer).
'white'+'admiral'='WHITE ADMIRAL'
Can you help me to learn more?
(Other definitions for white admiral that I've seen before include "Describing doctor's oath" , "Butterfly - with a Daimler (anag)" .)