This is the 20th mission also known as Episode 20 Voices. For this mission you will need to make your way through two outposts, then you will come to a bridge that has been destroyed. Make your way through the misty jungle, up and around towards the mission goal. Go inside the base to trigger the cinematics and afterwards run outside and run towards the tunnel. After the tunnel closes, you will want to use one of the water towers to extinguish the enemy. Once he is down call for extraction and get on the chopper.
If you're interested in watching an S Rank walkthrough of the mission, you can view the video below: