The fog came in slowly that evening, the way it always did in autumn, rolling over the harbour wall like a cat settling onto a blanket.

Biscuit watched it from the top of the lighthouse stairs, her tail curled neatly around her paws. Below her, the fishing boats were coming home one by one, their lanterns making soft yellow smudges in the grey.

“It’s only fog,” said Wren, though she said it softly, because the fog seemed to be listening.

She was at the little table by the window with a cup of tea going warm in her hands and the logbook open in front of her. Every evening she wrote the same kind of thing. Wind: light. Sea: calm. Lamp: lit. Cat: present. Tonight she added a line. Fog: thick, but friendly.

Somewhere out past the harbour, the old bell began to ring. Not loudly. Just enough.

Biscuit’s ears turned towards it like two small sails.

The fog bell had hung on the end of the breakwater for longer than anyone in the village could remember. It rang when the fog came and stopped when the fog went, and nobody had ever quite worked out who rang it. Old Mr Pennock said it was the tide. The postwoman said it was the wind. Wren had her own idea, which she kept to herself, and which involved a very old seal with a very good sense of timing.

“Shall we go and see?” she said.

Biscuit did not answer, because she was a cat, but she went down the stairs first, which meant yes.

Outside, the world had gone soft at the edges. The lamp above them swept its long slow arm across the fog, and the fog held the light for a moment before letting it go, and held it again, and let it go. Their footsteps on the breakwater sounded close and small. The bell rang. They walked towards it.

Halfway along, Biscuit stopped.

At the end of the breakwater, where the bell hung on its iron frame, there was a shape. It was round and grey and it was looking at them with two dark, patient eyes. Every time the swell lifted, it rose with it, bumped the bell gently with its nose, and sank back down again.

Dong.

“Well,” said Wren.

The seal looked at her. The seal looked at Biscuit. Then, with the air of someone who has been doing a job for a very long time and does not intend to be interrupted, it rose on the next swell and bumped the bell again.

Dong.

Biscuit sat down on the wet stone, which she would never normally do, and watched with great respect.

They stayed for a while. There was nothing to do and nothing to say, and that was the best kind of while. The lamp turned. The fog drifted. The seal kept its slow, careful time, and the boats in the harbour, hearing it, found their way home along the wall.

When the last lantern had gone in, the seal gave the bell one more push, a little softer than the others, and slipped under the water without a sound.

The fog began, very gently, to lift.

They walked back along the breakwater, Wren with her hands in her pockets and Biscuit just ahead, her tail up like a small flag. At the lighthouse door Wren stopped and looked out at the harbour, where the water lay dark and still and the moon was finding its way through.

“Fog: thick, but friendly,” she said. “Bell: seal. Cat: present.”

Inside, the tea had gone cold and the logbook was still open. Wren wrote her line. Biscuit climbed onto the blanket by the stove, turned around three times, and settled.

Out on the breakwater the bell hung quiet in the dark, and the tide came in, and went out, and came in.