Get involved with an intermediary (5)
I believe the answer is:
agent
'intermediary' is the definition.
(I've seen this in another clue)
'get involved with an' is the wordplay.
'involved with' indicates an anagram (involved can mean confusing or complex).
'get' with its letters anagrammed with 'an' can make 'AGENT'.
(Other definitions for agent that I've seen before include "Middleman" , "Salesman" , "Actors' manager" , "One does business on behalf of another" , "Factor, spy" .)