When the audience comes in to see The Stones (6)
I believe the answer is:
agates
'the stones' is the definition.
(I've seen this before)
'when the audience comes in' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'the audience' becomes 'gate' (I can't justify this - if you can you should believe this answer much more).
'comes in' is an insertion indicator.
'as' enclosing 'gate' is 'AGATES'.
'to see' is the link.
Can you help me to learn more?
(Other definitions for agates that I've seen before include "Hard coloured stones from a stage" , "Pieces of impure quartz used as gemstones" , "[RING]-fillers required" , "Multi-coloured quartzes" , "Stones to be found in a stage" .)