Note: Complete Mission 41, then complete Side Ops until you get sent back to Mother Base for a cutscene. This mission doesn't get graded like the other Main Missions.
|1||Identified the person who sent the transmission||Mandatory|
|2||Eliminated the infected||Mandatory|
This is a pretty linear mission, with really nothing in it that will make you deviate from the path set out for you. The important thing to remember is to not shoot anyone or you'll fail the mission. You can check the side rooms, but they don't really contain anything of importance, so keep following the path until you get to the top floor, where you'll find the person who sent the transmission.
Well, things have certainly turned for the worst, now. You need to make your way back down to the entrance, only this time you'll be asked to kill anyone who is infected. With your newly acquired goggles, you can see who is infected, although you don't really need it for now, so just shoot everyone you come by, as you won't be able to leave with them still alive.
Continue on, unfortunately having to shoot everyone in your way, until you come to the exit, which you can't open yet. That's because there's more infected to find, who are in the basement. Find the stairs leading down and open the door to find a lot more, but be careful here, as the guy on the floor isn't infected. Grab him and bring him to the exit, where you'll need to put him down to check again. Turns out that he is now infected, so set him down and gun him down, then leave the place to finish the mission.