The undead have been the most faithful companions and sources of the most reliable help for Mortimer and Benjamin. Perhaps that was because of the fierce bias had by so many towards them. Once getting past the smell, and the rot, the brothers hardly could find better or faithful friends. Often the abuse they had received gave them issues that had to be worked through. But once they could let go of their problems, they could be trusted with just about anything.
For some unknown reason zombies tended to emerge miraculously from Utah Valley. In time the brothers would learn that it was a natural consequence of some unusual practices that were engaged with by many people in the vicinity of northern Utah. So basically it was just due to the nature of the local community, and as there's not a lot a zombie can do to fit in in normal life, so they would hide and congregate in the caverns beneath the Provo Cemetery.
The first zombie to come to the Blackburn Boarding House was the maid, Babette. She would soon be followed by Zeddy Zorbingo, who was an expert gardener.
And it would be through Zeddy's cousin Victor that the brothers would have some of their most marvelous adventures down south; the one experience where they busted what would eventually amount to an entire community of the undead would live on in infamy for those who didn't understand.