Arrests party in police station (3,4)
I believe the answer is:
cop shop
'police station' is the definition.
(I've seen this before)
'arrests party' is the wordplay.
'arrests' becomes 'cops' ('cop' can be a synonym of 'arrest').
'party' becomes 'hop' (hop is a kind of party).
'cops'+'hop'='COP SHOP'
'in' acts as a link.
(Other definitions for cop shop that I've seen before include "'Police station (3,4)'" , "office investigating crime" , "Nick" , "Police station (slang)" .)