Arsenic and Old Lace — synopsis needed (8)
I believe the answer is:
scenario
'lace synopsis needed' is the definition.
I can't judge whether this definition defines the answer.
'arsenic and old' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'arsenic' is 'scenari' which is located in the answer.
'old' could be 'o' (abbreviation) and 'o' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for scenario that I've seen before include "Outline -- setting for a novel" , "plotting for a film" , "Story outline" , "Summary of plot of play" , "Storyline" .)