Keep mum in shot (5,2)
I believe the answer is:
close up
This clue is a double definition.
'keep mum' is the first definition.
('close up' can be a synonym of 'keep mum')
'shot' is the second definition.
(thesaurus)
'in' acts as a link.
(Other definitions for close up that I've seen before include "Cease operating; draw together" , "shut?" , "Photograph" , "detailed scrutiny" , "refuse to talk" .)