Dr. Emmerich wants to defect. Head to Serak Power Plant to make contact with him.
Metal Gear Solid 5: The Phantom Pain – Make Contact with Emmerich
Dr. Emmerich wants out of whatever it is he’s caught up in, so follow the marker to Serak Power Plant.
As you head towards the mission area, you’ll be waylaid by Quiet, starting off episode 11, so once that’s dealt with, get back on track and make your way to the power plant.
You need to reach the locked door at the other side of the area. Sneaking around either edge of the map is your best bet. You can clear out the soldiers if you like, but very shortly, you’ll be coming back through here and they’ll all respawn.
When you reach the locked door, you’ll initiate a cutscene. Watch it unfold, take care of the two soldiers in this area, then pop up the staircase to the right to grab the intel.