The surface of the beach has a crust of ice. It takes a lot to freeze seawater, but believe me, here in Eerie we have what it takes, and then some. We crunch our way out to the sea along the iron legs of the pier, the small lights of the town twinkling as they fall behind. Once we draw level with Seegol’s Diner – a last outpost of friendly warmth on the pier above – we are faced with the great void of nothingness beyond.

“Should we use our torches?” Vi shouts above the wind. “They’d be useful, but also a giveaway. Eels would see us coming a mile off.”

“It’s tempting,” I call back. “I can’t even see ten paces ahead, let alone all the way to the wreck. But I think we should let our eyes adapt, if they can.”

So we head on into the dark, sticking close together, hearing the wind whistling in the pier struts to our left, until even that is gone.

“Can you see anything?” I shout into Violet’s ear. The wind has become a roar.

I feel her shake her head.

“Except…” she says. “What’s that?”

“What?” I reply.

“That light. Over there. A purple light.”

I squint over to where I think Vi is pointing. A purple light?

And then I see it. A small point of light that bobs along like a will-o’-the-wisp, further up the beach, reflected faintly on the icy sand. And yes, purple.

“OK, that’s weird,” I say. “I … I don’t know what that is.”

“Whatever it is, it’s getting closer. Should we run?”

“Yes!” I shout, and we do, heading straight out towards the sea as fast as we can on the crusty sand. The purple light bobs a moment longer then flashes, as if it has seen us and wants a closer look.

“—LOOOOO!” comes a sound, hardly reaching us over the wind. “HALLOOOOOO!”

I grab Violet’s arm, and pull her to a stumbling halt.

“HALLOOOOOO!” I cry back, cupping my hands together.

“What is it?” gasps Violet.

“Not what,” I say with a grin. “Who. Look!”

And a figure steps forward into near visibility, just ahead of us. The purple light flashes up and picks out the features of a face we both know, muffled by several scarves and topped off with at least three hats, tied on with string.

“Mrs Fossil!” I cry. “Are we glad to see you! We thought we were about to be abducted by sea fairies or something.”

“Herbie, what are you doing out here?” puffs Mrs Fossil as she reaches us. “Don’t you know it’s the longest and darkest night of the year?”

“We could ask you the same question,” says Violet. “How’s your arm?”

“Oh, it’s not so bad,” says Mrs F. “A bit stiff, but I can still hold a bucket. It’s certainly not bad enough to stop me amber-hunting.”