So I dreamed the zombie apocalypse happened and had happened several years or even generations ago. There was a legend that someone had discovered a way to reverse the zombie plague (turn zombies back into people) so a group of people research the person who created the cure, and then much like a zombie DaVinci Code discover where the guy hid the cure or rather where the instructions to the cure were hidden. So the group of people sacrifice everything, even not worrying about companions being bitten because once they get the cure, they’ll be able to turn people back.
So they find the final resting place of the cure (a public bathroom hidden in the toilet paper dispenser) and open the container that should contain the instructions for the cure. It is in fact instructions on how to build an ark to save humanity. (I dunno if it was to send humanity to another planet or just put them in cryostasis and wait until the zombies die off.) See the legend began as this guy had a way to save humanity and over time people thought it was the cure for the zombie plague.