I do not expect a singleplayer campaign for this game, and neither should you. But what the fuck.
This takes place in a facility in the third quarter of the game. You were sent here to retrieve data(maybe stolen?) on ________
You walk into a room in a lab, and in the middle there is a (bulky/blocky)humanoid metal thing in the center with contrainsts and shit, with "Subject insert random letters/numbers here" engraved in it, and it's shaking a bit. There is a computer in one part of the room. You walk over to it, on a mission to retrieve data or whatever. After hacking into this to get the data, all the doors in the room slam shut and an alarm sounds with red flashy lights, "SYSTEM BREACH. EMERGENCY SECURITY SYSTEMS ACTIVATED". With steam and shit, the Bulky metal shit in the center of the room comes apart, and out of the smoke comes a huge muscular man with angry-ass eyes and a yellow liquid tank thing in his chest. A red liquid shortly mixes in to this(Die Hard much?), and he flips the fuck out. You successfully got to the data by the way, and it finishes downloading to your flashdrive or whatever in 60 seconds, and there is a 60 second timer near the thing on his chest. Your m9 and SA80 barely scratch him. You have to avoid him for 60 seconds, then a green liquid pumps into the thing on his chest, and he passes out. The doors open. You have to fight your way out of the facility, since they all know you're there now. You'll have trained zeds thrown at you, and other infantry, but you're mainly supposed to run the fuck away, since you aren't special in any way. You barely make it onto an evac chopper, and the game continues from there, according to whatever the fuck the main quest is.