Drop in demand! (4)
I believe the answer is:
call
I believe this is a double definition.
'drop in' is the first definition.
(thesaurus)
'demand' is the second definition.
(call is a kind of demand)
(Other definitions for call that I've seen before include "Ring; name" , "decision" , "Be in control" , "Shout - name" , "Hail; visit" .)