"That seems... unwise", said the human. "Vampires? I'm inclined to believe you are one, after seeing what I didn't believe could exist", referring to the zombie horde. "But the tales of vampires say you kill humans too. Now you want us to let a crowd of vampires into our compound? That sounds just as bad as falling to the zombies."

"It's true we, my kind, us vampires, feed on humanity", said the vampire. "But we are also pragmatic. We need human blood to survive. Zombie blood doesn't sustain us, it makes us sick. If the zombies win this war we will lose too, for a lack of blood. We are parasites. We don't want the host to die. Our interests align."

"Even if I agree, what help can you provide? There are tens, perhaps hundreds of millions of zombies. How many are you?"

The vampire's red eyes bore into the human's. "A scant few thousand. The stories about us have always overestimated our threat, to cower humans away from active resistance. But the zombies are mindless, driven by their ravening yearning for flesh and brain matter. We are not. Our strength is as the hurricane. And, you humans excel at tactical planning."

"A Faustian bargain indeed." Arms crossed, the human regarded the vampire with a calculating view. "Can you limit the amount of blood you drink? The stories say vampires completely drain blood, killing people."

"Yes. As I said, we are parasites. The loss of one human didn't used to matter, when you numbered in the billions. Now you do not. Killing one of you puts us in danger." What might have been a smile passed the vampire's lips. "Ask not for whom the bell tolls, it tolls for thee."