Every night, without exception, an old cat named Ptolemy walked the rooftops of the town of Mirham, counting sleeping children.

He carried a small scroll in his mouth — a tally sheet, rolled tight, on which he made one mark for every sleeping child he found. He moved from chimney to chimney, from gable to gable, peering through bedroom windows with his gold eyes, listening for the particular quality of breathing that meant deeply, safely, properly asleep.

When his count reached one hundred, he would sit at the topmost point of the town — the iron weathervane on Saint Merrin’s church — and close his eyes. This was the signal the stars had been waiting for. They would settle into their final positions, the night would close over the town like a warm hand, and everything would be exactly as it should be until morning.

He had done this every night for four hundred and thirty-seven years. He had never once reached a number less than one hundred. Until this particular Tuesday in October.

He counted carefully. He always counted carefully. He went street by street, house by house, the way a methodical creature counts the things it loves. He checked under blankets and behind curtains and did not count the dog on Wren Street even though it was very deeply asleep, because dogs, while admirable, were not part of his remit.

At the end of his circuit, he sat on the church roof and unrolled his tally scroll. Ninety-nine marks. He counted them again. Ninety-nine. He looked up at the stars. They were waiting, slightly impatient, in their almost-settled positions — not quite in place, not quite right, like a sentence missing its final word.

Ptolemy looked back at the town. Every window dark. Every house quiet. And yet: one child, somewhere, was not asleep.

He rolled his scroll back up and went to find them.

He found the window by the light. Not much light — just the thin gold line under a bedroom door that a child makes when they have pulled the blanket over their head and are reading with a torch they are not supposed to have.

The child’s name, Ptolemy knew from previous years, was Milo. He was six years old, had a gap where his front teeth should have been, and was currently on page forty-seven of a book about deep-sea fish.

Ptolemy landed on the windowsill without a sound. He looked through the gap in the curtain at the blanket-mountain that was Milo, with its telltale glow.

He could wait. He had patience the way old things who have kept vigil for centuries have patience — slow and deep and absolutely unshakeable. But the stars were waiting. And tomorrow was a school day.

He tapped the window. Once. Twice. With one careful claw.

“Are you real?” Milo whispered.

Ptolemy considered this question with the seriousness it deserved. Then he blinked — slowly, the way cats do when they mean to say yes, obviously, now stop asking foolish questions and go to sleep.

“Why are you at my window?”

Ptolemy lifted one paw and showed Milo the tally scroll. He held it up to the glass. Milo squinted at the ninety-nine marks, and then — because Milo was the kind of child who understood things quickly — he understood.

“I’m the missing one?”

Ptolemy blinked again. Something warm and particular passed between them through the cold glass — the feeling of being specifically, carefully, personally looked for.

Milo turned off his torch. He closed the book on page forty-seven — the anglerfish could wait. He lay down and pulled the blanket properly up to his chin and looked at the cat on the windowsill, who looked back at him with four-hundred-year-old golden eyes.

“Will you stay,” Milo asked, “until I’m asleep?”

Ptolemy set the scroll down on the sill, sat up straight with his tail curled neatly around his paws, and prepared to wait. He had waited for warmth to find its way home before. He could do it again.

Milo’s eyes closed. His breathing changed — slowly, slowly — into the deep particular rhythm of a child who is properly, safely, completely asleep. Ptolemy listened until he was certain. Then he picked up his scroll, made the hundredth mark, rolled it carefully, and went to his post on Saint Merrin’s weathervane.

The stars settled. The night closed over the town. Everything was exactly as it should be.

Below, on page forty-seven of a book about deep-sea fish, an anglerfish waited patiently in the dark — carrying its own small light in front of it, for exactly the same reason Ptolemy carried his scroll: so that things which are lost can be found.