Alright. The characters all graduated from school and were in the process of either getting their job assignments, going to their jobs, or just hanging out. Dan's character accidentally set off a revolution between the Ref (refugees from the Wasteland that entered the Vault 50 years prior to the events of this RP) and the Vault-born Security Force. The Ref group down in the Living Quarters managed to kill off a large number of Security Force Officers and then proceeded to head up towards the Overseers' (there was 2 Overseers) Offices. Now while the revolution was happening, a breed of monsters appeared in the Vault (there is speculation as to how they appeared and I hinted at it twice, but there is no explanation other than they just got into the Vault somehow) and they started by killing the Overseers. 

The Ref forces were almost entirely wiped out by these monsters and the, better armed, Security Forces are fighting the monsters but currently they are losing the battle. I believe that all of the characters have decided that it would be best to leave the Vault, for one reason or another, and they are now heading up towards the Vault entrance. As of now, no monsters have made their way up to the entrance because they are too busy slaughtering the rest of the Vault below.

So you could have your character come in really anywhere in the upper levels because the lower levels are just blood baths and filled with corpses from either the monsters or the civil war. I'll also give [b]everyone[/b] a rundown on the casualties so far.

[b]Ref casualties (including the Revolutionaries)[/b]
50+
70-80% of the Ref population is wiped out.

[b]Vault Dweller casualties[/b]
60-70+
50-60% of the Vault-born Citizens are dead.

[b]Vault Security Forces[/b]
6 are alive.

[b]Monsters[/b]
Estimated 10-15 of them in the Vault.
2 are dead. 
Numbers seemingly increasing as the battle goes on.