These words refer to secret plans contrived to attain some possibly improper or illegal goal. Intrigue stresses behind-the-scenes manipulations, but it may or may not imply impropriety or illegality: a court rife with intrigue against the emperor’s life; adept at the intrigue necessary to carry on a clandestine love affair; small-town intrigue that amounted to nothing more than trivial gossip. Intrigue may be a collective noun for the sum total of secret manoeuvring in a given social context. Machination more often refers, less inclusively, to a secret or semi-secret stratagem a devious action or an underhand manoeuvre that is part of a larger plan. It usually appears in the plural and suggests, disapprovingly, some impropriety of motive: machinations to make it appear that the innocent girl had committed the murder.

Plot suggests a specific, inclusive plan worked out in detail by a person or group, most often to gain some improper or illegal goal: the plot to assassinate Caesar; a plot to rig a union ballot. Intrigue or machinations may be resorted to as elements in furthering a plot or in its final carrying out. Both most often suggest subservience to the kind of master plan indicated by plot : certain that a plot of some sort was under way from the amount of intrigue he caught wind of.

A plot may sometimes be petty in scope, but conspiracy is applied chiefly to serious crimes, and there is something sinister about the word Specifically, in this sense, a conspiracy is a plot involving two or more persons who plan together to commit an evil or unlawful act: a conspiracy to overthrow the military junta; A team of special investigators uncovered a price-fixing conspiracy in the industry.

Scheme is much more general than the other words in this group. Nothing improper or illegal at all may be referred to; the word, in fact, might point exclusively to the devising rather than to the furthering or carrying out of a plan: suddenly coming up with a scheme that would solve their money problems. But scheme , unlike plan, often carries an unfavourable connotation, implying something underhanded and self-serving: the scheming Iago, devising a way to bring about his successful rival’s downfall.