Backdrop ready at last, screen adaptation is going ahead (7)
I believe the answer is:
scenery
'backdrop' is the definition.
(I've seen this before)
'ready at last screen adaptation is going ahead' is the wordplay.
'at last' says to take the final letters.
'adaptation' is an anagram indicator.
'is going ahead' says to put letters next to each other (some letters go in front of others).
The final letter of 'ready' is 'y'.
'screen' with letters rearranged gives 'scener'.
'y' after 'scener' is 'SCENERY'.
(Other definitions for scenery that I've seen before include "Landscape features" , "Stage sets" , "Stage setting" , "Items on stage" , "Attractive landscape" .)