conspire with (one)
To plot or scheme with one. What are you kids whispering about back there? You better not be conspiring with each other! The president of the company conspired with his assistant to conceal all evidence of his crime.
conspire with someone (against someone or something)
and conspire (with someone) against someone or somethingto join with someone in a plot against someone or something else. The CEO conspired with the board of directors against the stockholders. Ed conspired with Sam against the plan.