Co-narrate? Sure!
We'll filll the thread with complaints are gore.

How 'bout this:

No one knew where the zombies came from. No one expected them, and as such, no one was prepared. Within a few short weeks, countries were overrun, cities reduced to rubble, and those who managed to muster any form of resistance couldn't survive for more than a week.

The remaining humans gathered, and formed one last defence; a huge city, protected and guarded, with multiple walls and sentries, equiped with traps and devastating bombs. But it became apparent that it was more than just mindless zombies. Someone was controlling them, manipulating them, and that someone was a traitor, a survivor himself from the inside. How else could they explain how the zombies avoided the mass of landmines and buckets of molten iron? The zombies stuck at the weak points in the wall, and soon, most of the city crumbled. What is left is the core of the city. Humanity's remaining hope.