Involved in a score or film story (8)
I believe the answer is:
scenario
'film story' is the definition.
'scenario' can be an answer for 'story' (thesaurus). I am not sure about the 'film' bit.
'involved in a score' is the wordplay.
'involved' is an anagram indicator (involved can mean confusing or complex).
'in'+'a'+'score'='inascore'
'inascore' with letters rearranged gives 'SCENARIO'.
'or' is the link.
Can you help me to learn more?
(Other definitions for scenario that I've seen before include "Outline of film, novel, etc" , "Storyline" , "Projected sequence" , "plotting for a film" , "Summary of plot of play" .)