Tons are involved in crime (7)
I believe the answer is:
treason
'crime' is the definition.
(I know that treason is a type of crime)
'tons are involved' is the wordplay.
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'tons'+'are'='tonsare'
'tonsare' anagrammed gives 'TREASON'.
'in' is the link.
(Other definitions for treason that I've seen before include "Crime of treachery against the state" , "Betrayal of the state" , "Act of betrayal of a government" , "subversion" , "One's art? (anag)" .)