“Where are you now Twilight?” the voice of Celestia whispered into Twilight’s head. She couldn’t answer: she was standing on the edge of what was seemingly a large, vaulted cave, lost in darkness. The meagre light provided by the hanging torches behind her in the stairway were trying, unsuccessfully, to illuminate the first yard ahead.

“Shall I activate a light spell?” Twilight asked her mentor silently, using the telepathic link established between them.

“Yes, but a dim one only. Walk ahead very carefully. If my bearings are exact, you should encounter a wide chasm about halfway of this hall. Nothing you cannot jump over, but you must be proceed very, very gingerly.”

Twilight’s horn radiated a lambent light, and she tiptoed forward, her gaze locked on to the floor. Her hooves clanged on the uneven stones, a sound reverberated by the unseen walls around her. Suddenly, a few steps ahead, the ground vanished into nothingness. She stopped. “The chasm stands just before me.”

“It’s not large. You can fly over it. Don’t look down.”

Twilight took off and, in flagrant violation of Celestia’s order, hovered for a while over the gap, trying to figure out how deep it was. She blinked. At the far end of her field of vision, down into the gap, she’d seen something. A blurry, strangely twisted shape. Faint colours. A design. A design? Wait! A chill ran down her spine. Could it be…?

She shook her head and alighted on to the other brink. She’d a mission to focus on. Her imagination was running wild and she was seeing things, period. “What now?”

“Go ahead. No further hazards here. The far wall’s about thirty metres ahead.”

Twilight paced steadily, until a stone wall loomed out of the obscurity. “I’ve reached the far wall.”

“Very well. You should see three archways cutting through it. Don’t, I repeat, don’t choose the left one. It leads to a trap, you’d die. Now, for the two other ones, I can’t offer you any advice. You’re on your own.”

Twilight hesitated for a moment. “There’s foul air here. I’ll take the right one.”

“Good luck Twilight!”

Boldly, Twilight passed under the arch. Right behind was another stairway, hardly wide enough for her. If this was a cul-de-sac, she wouldn’t be able to turn round: she would’ve to climb upstairs backwards.

Downstairs, step by step. Breathe deeply. Let your eyes sweep the floor, the walls, the ceiling. Stop! She’d seen strange glyphs carved in the wall. “Magical runes!” She looked closer. “Unknown to me. Old. Worn away. Almost gone. Storing no perceptible energy.”

“Be very careful. It might be nothing, but it might be yet another trap,” warned the voice of Celestia.

Turning her attention to the stairs again, Twilight made a cautious step forward.

The slab clicked under her hoof, and the glyphs flashed.

Somewhere, behind her, something crashed on to the ground. And, with a loud rumble, began to… roll down? Quick! Escape! She concentrated, but nothing happened.

“Boulder behind me! Cannot teleport. The glyphs absorb my magic.”

“Run!” ordered Celestia.

Twilight took to her heels and rushed down the stairs as fast as she could. She had barely descended a score of steps that she almost crashed into a wall. “Dead end!” she yelled, panicked. “I can’t turn around, it’s too narrow.” The ominous rumble was rising to a din. “The boulder’s on me!”

“Twilight! Twilight?… Twilight?” shouted Celestia almost aloud. She waited for a short while, then sighed.

“What is it?” asked Twilight. “Don’t tell me…”

Celestia lowered her gaze and bit her lips. She shook her head, slightly. Taking a red pencil, she crossed out a small line on the map lying before her.

“Another one!” Twilight growled. “I can’t stand it any more. She was the twenty-first!”

“Twilight, we must force our way into Sombra’s den and recover this book, whatever the cost. It’s the only way to keep him at bay, forever.”

“Can’t we send royal guards instead?”

Celestia recoiled. “You must be joking. Guards are real ponies. These are just clones, bred for a very limited lifespan anyway.”

Twilight shuddered. “I know. But each time it’s like… It’s like I was actually dying. Why should you use me as a mould, and not you or Luna?”

“We are too big. Our replicas wouldn’t even pass the first room.”

There was a heavy hush, and eventually Twilight sighed. “All right, all right. Let’s go fetch the twenty-second…”