They repeated the experiment with a nail file, a bit of rolled-up paper, and Miss Drill's book, but no matter what object they used, the result was the same: it was whisked out into the grey void and vanished without a trace. On the last attempt, they both heard what sounded like a shriek amid the chorus of voices, and after exchanging a single horrified glance, slammed the shutters again. Mildred did up the latch and then leant against the wall on her side of the window, nursing a pinched finger and breathing hard.

"This is bad, isn't it?"

"Inelegantly phrased, but accurate," Constance said. She was feeling a bit breathless herself, but she was not about to let Mildred see that. She steepled her fingers under her chin while she thought a moment, and then said, "All right, the first thing to do is to find out whether we're completely surrounded by...whatever it is. You shall stay here while I go and look. Oh, good heavens, girl, don't shake your head at me that way. This room is the safest place in the castle—I've seen to that—and you'll be quite all right until I come back."

"It isn't that," Mildred said. "I'm not frightened of staying here on my own. I want to help. I won't do any magic if you don't want me to, but at least I can keep a lookout. You haven't been out there yet, Miss Hardbroom, but I have, and it's awful walking around in the dark with those voices whispering at you. Anything might happen."

Constance studied Mildred's face and saw nothing but earnestness and good intentions on it. From long, painful experience, she knew that Mildred's good intentions had a way of going awry, but against her better judgment, she yielded.

"Very well, Mildred." She picked up a lantern from her desk and lit the fat white candle inside with a spark from her fingertip, then lit one for Mildred as well. "Come along, and for goodness' sake don't touch anything or make a noise."

"No, Miss Hardbroom."

Lanterns in hand, they crossed the room and re-entered the tenebrous gloom of the corridor. The voices greeted them with even more urgency than before, and this time Constance thought she could understand snatches of their speech here and there.

... this

open...

...stop...stop...

...help me

why...

She glanced over at Mildred, who looked tense and watchful in the flickering candlelight, but Mildred still seemed to hear nothing but incomprehensible sounds. Clasped round the ring handle of her lantern, Mildred's hand sported ink smudges and bitten nails with traces of chipped green varnish, but it was steady and resolute as she held the light aloft, and Constance suddenly found herself glad to have the girl's company after all. It was not an emotion she had ever expected to experience, but there it was.

"Which way are we going?" Mildred asked.

"Up to the west tower," Constance said. "From the parapet we can see all round the castle at once, if we can get onto the walkway, that is. We shall have to be very careful going through the door. I don't know what happened to the things that were pulled through that barrier outside my window, and I don't care to find out."

"Neither do I," Mildred said with a shudder. "I'll follow you. The secret stairs are fastest."

The secret stairs were not really secret—when Constance had been a pupil at Cackle's, everyone had known about them by the end of their first term, and nothing had changed since then—but somehow the name persisted. In the castle's original incarnation, they had been a way to escape during sieges and uprisings, either by broomstick flight from the tower top, or by a network of underground tunnels that could be entered through the dungeon. Now they were mainly a shortcut that the girls used to get to lessons when they were late, and to visit their friends on other floors when they should have been sound asleep in bed.

Constance gave the concealed stone that opened the stairs a sharp jab, and a door swung silently toward them on hinges that each new generation of girls kept well oiled. As it did, she had a sudden, terrible moment of certainty that it would open on more of that grey blankness, and that she and Mildred would be trapped not only in the castle, but in this small section of it, forever. But all the door revealed was the dark passageway with its narrow, uneven steps winding upward, a hollow worn into the centre of each one by centuries' worth of treading boots. Damp, frigid air wafted out, and Constance shivered; ever since the night two years before when she had gone into a snowstorm to look for a monster, cold had made her feel uneasy.

"Are you all right, Miss Hardbroom?" Mildred touched Constance's arm lightly, and she shook off her nerves and took a firmer grip on her lantern.

"Don't be silly, Mildred, of course I'm all right. What are you waiting for?" She set a slippered foot on the first stair and began to climb with Mildred just behind her. In the close confines of the stairwell, the whispers should have been dulled, but they seemed as loud as ever in her ears.

can you...

...come...

...stop STOP...

...find that...

here...

...no!

Grimly, she climbed on, up and around the spirals one after the other. There were three hundred and twenty-three steps altogether, and long before they reached the trapdoor that opened onto the tower walkway, the muscles in her thighs and calves were on fire and begging for mercy. Even Mildred, who was put through worse paces several times a week during Miss Drill's P.E. lessons, looked as if her normally boundless energy were running out.

"I've never climbed all the way to the top in one go," Mildred said faintly. "It's farther than I thought. Can't you vanish us instead?"

"I don't dare 'vanish' anyone, Mildred, until I know it's safe in the place where I intend to reappear." Constance tried to keep her voice steady, but didn't succeed as well as she had hoped. "Keep climbing, girl. I'm nearly three times your age, and if I can do this, so can you."

They climbed on a few more steps, and Mildred said "Can I ask you something, Miss Hardbroom?"

"May I ask you, Mildred. Go ahead."

"Where did you learn how to vanish like that? I've never seen Miss Cackle or Miss Bat or Miss Crotchet do it."

"I learnt it from my tutor at witch training college," Constance said, thinking with an internal shudder of those endless lessons. It had been worth it in the end, but the process had been dreadful.

"Oh, her," said Mildred, and even though Constance could not see her face, she knew Mildred was scowling, a sentiment she heartily agreed with when it came to Mistress Broomhead. "Isn't there anyone else who can teach it? I remember you said a long time ago that we could learn one day."

Constance considered that as she forced her trembling legs up another step. Would it not be a coup if she could teach such a rarefied form of magic to Mildred Hubble, of all people? Even more, would it not go at least partway toward repairing what had been done to her if she could teach it without Mistress Broomhead's cruel methods?

"Mildred, if you pass all your subjects and exams this year, then I shall teach you myself when you're ready. Whether you are still a pupil here or somewhere else, you may come to me and I will see to it that you learn."

"Really? Do you promise?"

"Yes," Constance said. "And you know I always keep my promises."

"I know," Mildred said, and now there was a smile in her voice. "Thank you, Miss Hardbroom."

"You're welcome, Mildred Hubble," Constance said. "But you may want to save your thanks until after we have solved the problem at hand. Here's the trapdoor."

They had, indeed, reached the top of the stairs at last. Whoever had built them had seemed not to think it necessary to include any sort of landing; the steps simply got smaller and more oddly shaped until they dead-ended at the square wooden trap like something drawn by a surrealist. The trap itself was secured with three heavy iron bolts, each the thickness of a thumb, which slid directly into the stone blocks that formed the stairwell's ceiling and the floor of the walkway above. Constance passed her lantern down to Mildred, and holding onto the topmost step so as not to lose her balance, shot the bolts back one at a time. Then she pointed her fingers and sent a controlled stream of magic at the door, raising it just enough so she could peer through the opening.

...in here

...the...

take it...

...can't STOP

whispered the voices, and this time Mildred heard the words in the babble too and called "Miss Hardbroom!" from below.

"Yes, Mildred, I know," Constance said over her shoulder. "Hold the lights. Don't let them go."

"Can you see anything?"

Constance pushed the door higher and craned her neck, and her heart gave a sickening lurch in her chest. There was nothing but more grey void above.