In cahoots

In cahoots means in an alliance or partnership. In most contexts, it describes the *conspiring activity of people up to no good*.

There’s also the rare idiom go cahoots, meaning to enter into a partnership.
“Cahoot” may derive from French cahute, meaning “cabin” or “hut,” suggesting the notion of two or more people hidden away working together in secret. “Cahute” is believed to have been formed through the combination of two other words for cabins and huts, “cabane” and “hutte.”

Example

For some reason he blames me—like you and I are in cahoots to get him.

The actors, who were in cahoots with the bride and groom, attempted to pull pranks on the wedding party and guests.