Gangster in house, different mould (7)
I believe the answer is:
hoodlum
'gangster' is the definition.
(I've seen this before)
'house different mould' is the wordplay.
'house' becomes 'ho' (abbreviation for house).
'different' indicates an anagram.
'mould' anagrammed gives 'odlum'.
'ho'+'odlum'='HOODLUM'
'in' acts as a link.
(Other definitions for hoodlum that I've seen before include "Lawless youth" , "Street bully" , "Tearaway" , "Yobbo" , "Rowdy" .)