Conspiracy of silence revealed by newcomer talking (6)
I believe the answer is:
omerta
'conspiracy of silence' is the definition.
(I've seen this before)
'revealed by newcomer talking' is the wordplay.
'revealed by' says the answer is hidden in the clue.
'OMERTA' is hidden within 'newcomer talking'.
(Other definitions for omerta that I've seen before include "Mafia code of silence; at Rome (anag.)" , "Mafia code of silence, never inform" , "Mafia pledge of silence" , "conspiracy of silence" , "vow of silence" .)