Once you unlock the side op ‘Make Contact With Huey Emmerich,’ you’ll immediately be given access to the Serakh power plant, provided you’ve already completed you encounter with Quiet at the ruins. This mission isn’t exactly a walk in the park, but with a little patience and knowledge of the route you want to take, you’ll be able to get through this operation rather stealthily.
As soon as you drop at the landing zone and make your way to the power plant, crawl on the ground to avoid getting spotted by the guard with the searchlight. On the right side of the road, there’s a slope that leads up to a long metal platform, which you can use to enter the area undetected. Once you get past the searchlight, things get considerably easier. Aside from one or two guards patrolling the area up ahead, there’s very little standing between you and the small red door that lies at the northern end of the power plant.
Once you unlock the door, a cutscene will play, introducing you to Huey Emmerich. However, before you can extract him, he’ll be transported to a Soviet base nearby, thus beginning ‘Episode 12: Hellbound’, which is a main op. Carefully crawl your way back to the door you came in by, and Kaz will warn you about the presence of an enemy gunship. Just lay flat on your belly and keep crawling until you reach the door.
If you’re lucky, a sandstorm will come your way, masking you and your footsteps, and giving you an easier time getting out of the power plant. Simply exit the way you came, and call your horse so you can ride the rest of the way to the Soviet base.