Trouble arising in papers? It's a long saga (5)
I believe the answer is:
iliad
'a long saga' is the definition.
(ancient poem)
'trouble arising in papers?' is the wordplay.
'trouble' becomes 'ail' (synonyms).
'arising' shows that the letters should be reversed in order.
'in' means one lot of letters goes inside another.
'papers?' becomes 'ID' (identification papers).
'ail' written backwards gives 'lia'.
'lia' placed into 'id' is 'ILIAD'.
'it's' is the link.
(Other definitions for iliad that I've seen before include "Homer's work" , "Epic poem attributed to Homer" , "epic work" , "long story" , "Homer's ancient Greek epic" .)