Is there a word that means scheme or conspiracy, but slightly stronger than that? Like a word you would use to describe an evil murder plot/plan.
Context: Macbeth plans to kill Duncan for throne
In many historical dramas I see "coup" used as well as "overthrow." It depends on the context of the evil plan and what's expected or going to happen. You might even use "revolution" if a kingdom or country is headed towards the wrong direction by nobles or others. Otherwise a revolution could imply a change socially, culturally, technologically, etc. but it could be for the worse rather than improvement of society.
I'd prefer to use "collusion". Webster's dictionary defines collusion as
secret cooperation for an illegal or dishonest purpose.
Perhaps "Connive" could fit in some situations. It certainly depends on the context, but I think is stronger than "scheme."
Connive: (verb) to secretly help someone do something dishonest or illegal M-W