To start the CIA mission you first must go to the apartament where PSR is fighting the commies. If you don't aleready know you cang get there by going to the left when exiting the train station.

When you arrive you need to tell the Polish commander that you are there not to help, then kill all three Poles. After that The commies will ask if you came to help, say no and kill them all. After you do that, CIA will call you and offer you the job

You must go to the communist hideout on the right side of the map and retrive the orders.
You can obtain them in two ways:

-loot them from the commisar
-hack a computer to open a cell with a locker, you can find the orders there

Simmilar to the communist route you must infiltrate the power plant. Unlike the commie path you don't need to plant the bombs, only unlock the elevator and go up to the big computer room. You will find hackable computer where you need to install a virus. It's the same computer which you use to overload a reactor in the commie path.

After all your tasks are done, return to the commie hideout, then you will find a path with two grenade traps. You need to go through that path until you end up in a place with stairs and a ladder. Climb up to the joycultist base where you need to fight it's inhabitants. Make sure to grab a keycard, which you can find:

-on a table near TV
-on the armoured cultist's body

Climb up to the roof where you'll find entrance to the grainery tower. Enter it and go left, where you'll find an agent, tell the agent that you have finished the job and the level ends