Advise re FBI involvement (5)
I believe the answer is:
brief
'advise' is the definition.
(thesaurus)
're fbi involvement' is the wordplay.
'involvement' indicates an anagram.
're'+'fbi'='refbi'
'refbi' is an anagram of 'BRIEF'.
(Other definitions for brief that I've seen before include "Case given to a barrister" , "brusque > QC, perhaps" , "Remit" , "Brusque - lawyer (slang)" , "put in the picture" .)