Agatha pulled a rune-inscribed dagger from her purse. Her young companion did not look very surprised. It was a well-known fact that almost anything could be in a woman's purse, stuck in between squished tissues, lost change, and ancient, slightly decayed lipstick. It just so happened that he knew Agatha's purse was also full of charms, amulets, and the occasional talisman.
Ten years ago, Agatha has been a hellblazer, and her companion a bright young thing with high hopes of an apprenticeship. She had gone silver early, he had been her golden boy. They blitzed through the sexual tension in a whirlwind of will-they-won't-they bad relationships, empty bottles of wine set out for recycle, and had settled in to something as sexless and platonic as a Boston marriage. So they were, in the tunnel that had opened up in the cellar where the wall had fallen down, to see what was about.
Agatha muttered something vile in Anglo-Saxon as she cut a figure in the dark air, the runes glinting on the dagger. It wasn't, he reflected, a very good dagger to begin with. It had started off life as a Mosin-Nagant bayonet, one of those steel spikes with a screwdriver tip that the Russians had produced in their millions, and had been retrofitted with a solid steel handle and several lines of finely etched runes. You had to call them runes, because they were spiky and angular and clearly some kind of writing, but this wasn't your average Futhark. They were were the kind of thing H. R. Giger might have come up with if Tolkien's estate had commissioned an alphabet.
The earthen tunnel couldn't have been that old - there were bits of brick and masonry stuck in the side, though in London that pretty much just narrowed it down to sometime within the last fifteen centuries or so - but it opened up at last to a kind of cavern or space. Foul-smelling water flowed in a trickle from one hole in the wall and out another, and beyond it...
The thing chained to the wall was predominantly female. Tits were one of the few constants, though the number, shape, and size varied as it worked through a constant slow metamorphosis. It was, to him, like a slow .gif on 4chan, rotating through every fetish known or suspected to man. Hips swelled and sprouted fur, then shed and revealed patches of scales; the tongue flicked and swirled, the mouth sometimes wide and generous, then too wide, slipping into a bloody Glasgow smile that seemed to still be lascivious even through the gone, and then it was a spiked penis-thing, slipping through the ruined cheek, her face fucking itself...
Agatha's free hand reached back and grasped at him, found his hand and clutched it tightly. The one constant to the creature was the length of chain around the creature's neck, which was secured to a great stone in the ceiling.
"A succubus," Agatha said, holding the dagger in front of her. "Well, dear. What do I call you?"
The pale pot-belly shifted, eyes blinked open, a long flat nose; an alive complexion spread over it like a rash as hints of a skull an jaw pressed against the unbroken skin. Something down below was serving as a mouth as it spoke.