Almost all in first class for the last scene (6)
I believe the answer is:
finale
'the last scene' is the definition.
(I've seen this before)
'almost all in first class' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'in' means one lot of letters goes inside another.
'first class' becomes 'fine' (fine can mean fancy or first class).
'all' with its last letter taken off is 'al'.
'al' going within 'fine' is 'FINALE'.
'for' acts as a link.
(Other definitions for finale that I've seen before include "Last item of event" , "Conclusion of a performance" , "Conclusion, end" , "Last act, movement" , "Last section of a musical composition" .)