But the sound of his voice made the unicorn feel as though she were trapped forever, and once more she began pacing her cage, moving to keep her heart from bursting with the terror of being closed in. Rukh was standing before a cage that contained nothing but a small brown spider weaving a modest web across the bars. “Arachne of Lydia,” he told the crowd. “Guaranteed the greatest weaver in the world‌—‌her fate’s the proof of it. She had the bad luck to defeat the goddess Athena in a weaving contest. Athena was a sore loser, and Arachne is now a spider, creating only for Mommy Fortuna’s Midnight Carnival, by special arrangement. Warp of snow and woof of flame, and never any two the same. Arachne.”

Strung on the loom of iron bars, the web was very simple and almost colorless, except for an occasional rainbow shiver when the spider scuttled out on it to put a thread right. But it drew the onlookers’ eyes‌—‌and the unicorn’s eyes as well‌—‌back and forth and steadily deeper, until they seemed to be looking down into great rifts in the world, black fissures that widened remorselessly and yet would not fall into pieces as long as Arachne’s web held the world together. The unicorn shook herself free with a sigh, and saw the real web again. It was very simple, and almost colorless.

“It isn’t like the others,” she said.

“No,” Schmendrick agreed grudgingly. “But there’s no credit due to Mommy Fortuna for that. You see, the spider believes. She sees those cat’s-cradles herself and thinks them her own work. Belief makes all the difference to magic like Mommy Fortuna’s. Why, if that troop of witlings withdrew their wonder, there’d be nothing left of all her witchery but the sound of a spider weeping. And no one would hear it.”

The unicorn did not want to look into the web again. She glanced at the cage closest to her own, and suddenly felt the breath in her body turning to cold iron. There sat on an oaken perch a creature with the body of a great bronze bird and a hag’s face, clenched and deadly as the talons with which she gripped the wood. She had the shaggy round ears of a bear; but down her scaly shoulders, mingling with the bright knives of her plumage, there fell hair the color of moonlight, thick and youthful around the hating human face. She glittered, but to look at her was to feel the light going out of the sky. Catching sight of the unicorn, she made a queer sound like a hiss and a chuckle together.

The unicorn said quietly, “This one is real. This is the harpy Celaeno.”

Schmendrick’s face had gone the color of oatmeal. “The old woman caught her by chance,” he whispered, “asleep, as she took you. But it was an ill fortune, and they both know it. Mommy Fortuna’s craft is just sure enough to hold the monster, but its mere presence is wearing all her spells so thin that in a little time she won’t have power enough left to fry an egg. She should never have done it, never meddled with a real harpy, a real unicorn. The truth melts her magic, always, but she cannot keep from trying to make it serve her. But this time—”