The lowdown from inside grand opera ... (4)
I believe the answer is:
dope
'the lowdown' is the definition.
(I've seen this before)
'from inside grand opera' is the wordplay.
'from' indicates the answer is hidden within the clue.
'DOPE' is hidden in the letters of 'inside grand opera'.
(Other definitions for dope that I've seen before include "Aircraft fabric varnish" , "Idiot; information" , "grass, perhaps" , "Drug - information" , "Illegal drugs; fool" .)