Wise guys' initial gathering around chimney (10)
I believe the answer is:
illuminati
'wise guys'' is the definition.
(illuminati can mean wise or enlightened people)
'initial gathering around chimney' is the wordplay.
'gathering' indicates an anagram (letters gathered in a new way).
'around' is an insertion indicator.
'chimney' becomes 'lum' (Scottish word for a chimney).
'initial' anagrammed gives 'ilinati'.
'ilinati' going around 'lum' is 'ILLUMINATI'.
(Other definitions for illuminati that I've seen before include "Claimers of special knowledge" , "clever people" .)