Two bishops in sober company: Swedish group (4)
I believe the answer is:
abba
'swedish group' is the definition.
(Swedish band)
'two bishops in sober company' is the wordplay.
'two bishops' can mean two substitutions for 'bishop'.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'bishop' becomes 'B' (abbreviation for bishop in chess).
'in' is an insertion indicator.
'sober company' becomes 'AA' (Alcoholics Anonymous).
'b'+'b'='bb'
'bb' put into 'aa' is 'ABBA'.
(Other definitions for abba that I've seen before include "camel-hair coat" , "Biblical father" , "Renowned Swedish foursome" , "6 24 113 [SCAN-DIN-AVIAN] band" , "striped coat?" .)