Advanced inside information followed by heartless city operation (6)
I believe the answer is:
agency
'operation' is the definition.
(thesaurus)
'advanced inside information followed by heartless city' is the wordplay.
'advanced' becomes 'a'.
'inside information' becomes 'gen'.
'followed by' means one lot of letters go next to another.
'heartless' means to remove the middle letters.
'city' with its centre taken out is 'cy'.
'a'+'gen'+'cy'='AGENCY'
(Other definitions for agency that I've seen before include "Recruitment bureau" , "Business that conducts business on behalf of others" , "Through which something is accomplished" , "Business serving other businesses" , "Bureau; action" .)