They start out as ritual magicians, thinking furious blue soundscapes in their minds until they invoke something. Which sticks around and, shall we say, gives them certain powers. It’s a symbiote, in other words, not a regular parasite. As long as they feed it, it stays happy and gives them a laundry list of handy tools. Super-strength: check. Good night-vision: check. Longevity: check. You-gotta-believe-me charisma: check. Good skin tone: check. A tendency to burst into flames if exposed to intense ultraviolet light . . . well, there are always drawbacks. But the important takeaway point is that they’re not walking corpses. They’re real live human beings, albeit immune to soul-eating (whether by me or by the feeders in the night), just like the people whose blood they get off on drinking . . .

. . . Although the hosts don’t stay human for long, once the V syndrome symbiotes use the sympathetic link the blood meal provides to latch onto their gray matter and chew holes in it.

You can’t catch vampirism from a vampire’s bite: all you can catch from it is a horrible lingering death. It can sometimes take up to six months for a host to die of V syndrome. But if too many symbiotes snack from the same juice bar, the deterioration takes off like a forest fire. That’s why the Scrum triggered the Tower Hamlets spike. If it was just one vampire, feeding on one victim, we might never have noticed. We might have mistaken it for part of the constant background rate of Creutzfeldt-Jakob disease.

Vampirism is, thankfully, extremely rare. Traditionally it took a ritual magician of some power, performing a major invocation that pushed back the frontier of the art, to attract the attention of the V syndrome symbiotes. And he or she would usually last until the first sunrise—either by accident or design. Most non-psychopathic practitioners who realize what they’ve become recognize the side effects and their likely fate immediately. They commit suicide rather than inflicting the cost of their survival on others, or pay the hideous price of abstinence.

Which is why most long-term surviving vampires are psychopaths.

What are the traits of a successful vampire, a long-term survivor?

Well, they have to be a conscienceless killer, willing to accept the slow, cruel destruction of others’ lives to fuel their own continual existence.* They’d have to be wealthy in order to finance the regular changes of identity necessary to conceal their longevity, and to buy the immunity from scrutiny that the eccentricity of their lifestyle demands. They’d have to be very intelligent and ruthlessly dedicated to keeping their existence a secret, because they are by definition a serial killer: one who can go no more than six months between victims. And they’re a ritual magician of considerable power who is now immune to K syndrome parasites, the main brake on the ambitions of such practitioners.