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 explain this - if you can you should believe this answer much more).
'comes in' means one lot of letters goes inside another.
'as' enclosing 'gate' is 'AGATES'.
'to see' acts as a 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" .)