Stern detectives seen in burial ground (9)
I believe the answer is:
graveyard
'burial ground' is the definition.
(synonyms)
'stern detectives' is the wordplay.
'stern' becomes 'grave' (grave can mean stern or severe).
'detectives' becomes 'Yard' (Scotland Yard, Metropolitan Police HQ).
'grave'+'yard'='GRAVEYARD'
'seen in' is the link.
(Other definitions for graveyard that I've seen before include "church ground" , "Burial ground" , "Cemetery" , "remains here" , "Final destination" .)