China at last discovered secret group (6,3)
I believe the answer is:
dinner set
'china' is the definition.
(I've seen this before)
'last discovered secret group' is the wordplay.
'last' suggests the final letters.
'secret' becomes 'inner' (as in one's inner thoughts).
'group' becomes 'set' (both can mean a collection).
The last letter of 'discovered' is 'd'.
'd'+'inner'+'set'='DINNER-SET'
'at' acts as a link.
(Other definitions for dinner set that I've seen before include "Collection of plates and dishes" , "China" , "might be taken out for a meal" , "Table service" , "Plates etc" .)