“Promise me you won’t . . .” her father said, and pointed at his ear. (He didn’t know what to call the thing she did, and didn’t like talking about it in any case.)

“I promise,” Lavinia said, fingers crossed behind her back.

The doctor kissed his children, hefted his bags, and went. He’d only been gone a few hours when there was a knock at the door. Lavinia opened it to find a miserable young woman standing on the porch, pale as death, her haunted-looking eyes ringed by dark circles. “Are you the one who can take away nightmares?” she asked meekly.

Lavinia showed her in. Her father’s office was locked, so Lavinia brought the young woman into the sitting room, laid her down on the couch, and proceeded to pull a huge quantity of black thread from her ear. When she was finished the young woman wept with gratitude. Lavinia gave her a handkerchief, refused any payment, and showed her to the door.

After she’d gone, Lavinia turned to see Douglas watching from the hall. “Papa told you not to,” he said sternly.

“That’s my business, not yours,” Lavinia answered. “You’re not going to tell him, are you?”

“I might,” he said nastily. “I haven’t decided.”

“If you do, I’ll put these right back where I found them!” She held up the wad of nightmare thread and made as if to stick it in Douglas’s ear, and he fled from the room.

As she stood there, feeling slightly bad for having scared him, the thread in her hand rose up like a charmed snake and pointed down the hall.

“What is it?” she said. “Are we going somewhere?”

She followed its lead. When she came to the end of the hall, it turned and nodded left—toward her father’s office. Arriving at the locked door, the little thread strained toward the lock. Lavinia lifted it up and let it worm inside the keyhole, and a few moments later the door came open with a click.

“My goodness,” she said. “You’re a clever little nightmare, aren’t you?”

She slipped inside and closed the door. The thread slid out of the lock, dropped into her hand, then pointed across the room toward the drawer where her father had stashed the other threads. It wanted to be with its friends!

She felt briefly guilty, then chased the feeling away—they were only reclaiming her rightful property, after all. Crossing to the drawer, her thread repeated its trick on the padlock that secured it, and the drawer slid open. Upon seeing each other, the new thread and the old tensed and reared back. They circled each other on the desk, tentative, sniffing each other like dogs. Then each seemed to decide the other was friendly, and in a blur they meshed together to form a fist-sized ball.

Lavinia laughed and clapped her hands. How fascinating! How delightful!

All day long people came to the door seeking Lavinia’s help: a mother tormented by dreams of a lost child; small kids brought by anxious parents; an old man who each night relived scenes from a bloody war he’d fought half a century ago. She drew out dozens of nightmares and added them to the ball. After three days the ball was as large as a watermelon. After six it was nearly the size of their dog, Cheeky, who bared his teeth and growled whenever he saw it. (When the ball growled back, Cheeky dove out an open window and didn’t come back.)