Behind the laundromat, where there had always been a plain brick wall, Milo found a little door no taller than he was. He ducked inside. A small clockwork librarian slid a card across the counter. Tiny gears ticked inside her chest. "We lend tomorrows here," she said. "Borrow one good day from your own future and spend it today. Just return it by the deadline on the card."

Milo took the card. Tomorrow was his big science fair, and he wasn't ready. "I want a perfect day," he said. "One where everything goes right." The librarian nodded and stamped the card. Right away his backpack felt lighter and his head felt clear. "Spend it well," she said.

Everything went right all day, which felt strange. Milo aced a quiz he hadn't studied for. He caught a falling glass before it broke. Then he found something odd in his pocket: a second card, blank except for one word. "More," it said.

Milo tore up the "More" card. He didn't want to get greedy. The pieces turned to dust and blew away. At sunset he paid back his one borrowed day with a quiet Wednesday, and the librarian nodded. "You learned the most important rule," she said. "Borrow little. Live the rest."