Her crystal-clear reflection magically appeared in the mirror, dressed in Evil’s uniform—only it was her usual girl self, instead of a boy.

“Old with Old,

New with New,

Back to your tower

Before—”

Her reflection peered at her. “Wait a second, lad . . . you’re not a student here at all.” Her face darkened. “Intruder.” Her reflection opened her mouth wide. “INTRU—”

“No! It’s me!” Agatha yelped. “It’s Agatha!”

“All I see is an underfed, googly-eyed boy,” her reflection said, opening her mouth again to scream—

“I’ll prove it!” cried Agatha, knowing she had no choice now. She closed her eyes, visualizing the counterspell. . . . Her hair began to thicken, her jaw to round, and all at once her body eased back into her girl’s shape, filling out her uniform. “See. Me,” she smiled, now matching the reflection in the barrier. “So let me pass—”

“Oh. You,” her reflection growled, not smiling back. “You nearly got me destroyed for confusing the sides the past two years. First you convinced me you were Evil, when you were Good. Then you convinced me you were a Boy, when you were a Girl. No way are you getting past me a third time. So listen clear:

“Old with Old,

New with New,

Back to your tower

Before I call You-Know-Who.”

Agatha tightened. Out of the corner of her eye, she could see the chocolate patterns in the sky starting to evaporate. The sound of guards storming to the rooftop amplified inside the castle.

“And how do you know I’m not supposed to be on the Old side instead of the New?” Agatha asked her reflection, trying to stay calm.

“Easy,” her image huffed. “Because you’re as young as me and I’m as young as you.”

“So if I’m young, I can’t be old?”

“Have you ever met an old person who’s young?” her reflection fleered.

“Well. Would a newborn baby see me as young or old?” said Agatha.

“Old, but that’s because it doesn’t know any better—”

“So what about a child?”

“Depends on how old the child is,” her reflection snapped.

“So how young or old you are ‘depends’ on things?” Agatha asked.

“No! It’s obvious to anything that’s full-grown!”

“What about a full-grown flower? Or a full-grown fish?”

“Don’t be stupid. A flower or fish can’t see age,” said her reflection.

“But you said anything full-grown—”

“A full-grown person!”

“So you’re a person, if it’s obvious to you,” reasoned Agatha. “Yet you’ve been on this Bridge for thousands of years. So what does that make you? Young or old?”

“Old, of course,” her reflection puffed.

“And if you’re me and I’m you, then what does that make me?” Agatha said, lips curling to a smile.

Her reflection gasped, realizing the answer. “Definitely old.”

Agatha’s mirror image could only gape in anguish, fading into night, as the real Agatha reached her fingers through the barrier and felt the cold, empty wind.

Seconds later, the monstrous shadows swarmed to their post and saw nothing on the Bridge but a glint of black and green sliding into the castle, which they thought an errant piece of mist blown from the bay.