. . .
A couple of weeks went by, and it seemed pretty normal. Surprisingly, there was enough food and water for everyone in the city, and it was well protected from the zombies.
At this point, there were about several hundred Zombies who found out about the underground city and were trying to get in. Fortunately, the entrance had been blocked off, so they COULDN'T get in. All citizens were required to wear earplugs when near the entrance, to prevent from hearing the zombie's moans, so they wouldn't go insane.
One day(probably on a Tuesday), there was a loud commotion right outside the city entrance, and huge gunfires could be heard. Multiple zombies started falling to the ground and staying on the ground.
Only after 5 minutes, there seem to be more people on the other side, aiding in the fight.
Now there was a group of unidentified people right outside the entrance of City 5, killing all the zombies.
One had a blade,
One with explosives,
Another using a gun,
And another throwing both acid and fire.
It took literally 30 minutes until every zombie was killed, and a very familiar(to you) voice yelled, "They're all dead! You can open the entrance now!"
After it opened, Cassiopeia, along with 2 other people, walked into the city. "I don't want anyone asking me about this," she said.
...aaaaand in the background the forth person was burning all the zombies-