Scheme one's involved in leads to trial (5)
I believe the answer is:
pilot
'trial' is the definition.
(synonyms)
'scheme one's involved in' is the wordplay.
'scheme' becomes 'plot' (plot is a kind of scheme).
'one' becomes 'i' (Roman numeral).
'involved in' is an insertion indicator.
'plot' enclosing 'i' is 'PILOT'.
'leads to' is the link.
(Other definitions for pilot that I've seen before include "Steer, test (scheme)" , "Aircraft captain" , "Person in charge of aircraft" , "Plane operator" , "Plane flier" .)