I'm not well versed in X-COM lore, so bear with me.
You are human scientist, ADVENT employee number you never bothered remembering.
You exit research felicity to take the bus home, you say good bye to the big
yellow snake lady that is at the door (She is nice to you... You think..). As
you do she grabs her head and starts screaming.
You watch in horror as she falls to the ground and writhing in pain, scratching
her neck.
You walk over to her to ask what's wrong when you see an other of the big snakes
doing the same a around the corner that was hidden before.
You feel panic. You walk over to the closest one and try to talk to her, but she
does not respond, then she ceases to move.
She looks at you, puts up a hand to your face and hisses something in her
language that you don't understand, you swear she is smiling. Then she goes
limp.
She is still breathing. You need to get her inside, but you are not strong
enough to do it yourself. You call for help.
You see another human rush out of the felicity and he helps you bring in the
vipers and put blankets over them, making sure they are conferable.
You try to contact ADVENT but you get no response. The TV channels are all
static.
Days go by.
You and a few other scientists take turn guarding the vipers and the felicity.
Then one of the Vipers wakes up, she looks confused. Hissing something, as
points to her neck.
She's doing a cutting motion with her hands.
She wants you to cut her neck?
You talk to one of the few people that have medical training to do it. He
obliges after some motioning from the snake and your convincing.
You can't watch.
The guy comes out holding in his hand a small device, about twenty five
millimetres in diameter. He tells you it was connected to the spinal column and
had tendrils going up to the brain. But it was now removed. The Snake is fine.
A day later the Viper wakes up and she seems very thankful for what you and the
medic did.
As the days go by more snakes wake up, but the first snake talk to them, holding
a gun to them. Some are very nervous others hostile.
The ones that are hostile she leads to a room, and only she returns... You don't
dear go in there.
The ones that are left have similar devices removed from their necks, most of
them survive.
The first snake finds some paint and starts to make big crosses over any advent
symbol she can find. She hisses orders and others follow suit.
Their armour is re-painted in white.
You, the other scientists and the snakes are now foraging for food where ever
you can find it. It does not look good, the city is all but abandoned.
You find pockets of people, and a many dead troopers and a few dead vipers,
looks like they were fighting each other.
You help those you can.
You have now realised what has happened. ADVENT has fallen.
The old administrative building is full of dead people, vipers, troopers, what
have you. The Advent logo has been blasted from the wall on the outside, logos
inside pulled from walls.
The first viper (You call her Number One) spits at the logo.
It's been a month now, you and the rest of the survivors have cleared out the
administrative building and started to try to make things sort of work again.
The last of the ADVENT loyalists have been rooted and executed. (You are
thankful you did not have to watch).
A few Mutons are helping with clearing and building. (Not many Mutons survived
whatever it was that happened).
You have a working pseudo government in place in the city. People have gone out
and started to track down other serving cities and towns, to get food and other
necessities that are surely needed.
You and Number One have been put in charge of everything until things go back
to some semblance of normality. She understands you, but she can't speak, thus
she uses pieces of paper with words phases on them, and even writes on a white
board when you communicate.
Then is when they came... X-COM.
If you had any word for them it would be "devils".
They demand that you hand over the "xeno scum".
Number One is sombre. She sits quietly as you tell the X-COM bastard to shove
it.
She puts up a hand after a while, and writes on her small whiteboard.
She holds it up and you feel cold. "If that is what is needed to save these
people from more conflict."
You protest. She just puts a hand on your shoulder. shaking her head.