Secret agreement especially in order to do something dishonest or to trick people.
The act of doing something secret or illegal with another person, company, etc. in order to deceive people.
The police were corrupt and were operating in collusion with the drug dealers. (Oxford)
There was collusion between the two witnesses (= they gave the same false evidence). (Oxford)
operating in collusion
collusion between the two witnesses
Scheming
Collaboration
Exposure,
Betrayal
Collusive