Honour friends with fellow investigator (9)
I believe the answer is:
ombudsman
'investigator' is the definition.
(I know that ombudsman is a type of investigator)
'honour friends with fellow' is the wordplay.
'honour' becomes 'om' (Order of Merit).
'friends' becomes 'buds' (I've seen this in another clue).
'with' means one lot of letters go next to another.
'fellow' becomes 'man' (fellow can mean a man).
'om'+'buds'+'man'='OMBUDSMAN'
(Other definitions for ombudsman that I've seen before include "Public official" , "Commisioner" , "Maladministration investigator" , "Official investigator of complaints" , "Government appointee who investigates complaints" .)