Airmen involving one in schemes
I believe the answer is:
pilots
'airmen' is the definition.
(pilot is a kind of airman)
'one in schemes' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'schemes' becomes 'plots' (plot is a kind of scheme).
'i' inserted inside 'plots' is 'PILOTS'.
'involving' is the link.
(Other definitions for pilots that I've seen before include "They operate flying controls" , "Aviators and ships' guides" , "People who guide ships going into or out of a harbour" , "Fliers or guides" , "They fly planes or guide ships" .)