But Violet turns on her torch and the inside of the turret is lit again. The creatures writhe, creeping over my shoes, and I kick them off frantically. But with a longer, more stable light, I also get a sense of the interior of the turret as a space where men once worked, manning the gun. It calms me a bit to think of that, and I manage to brush a lobster off my leg with only a small whimper. And then I notice that Violet is shining her torch on something specific.

It’s an opening in the floor of the turret. A round opening, with metal foot- and handholds descending down into the belly of the ship.

“It’s another way in,” she says, picking a shrimp out of her hair and releasing it into a pool. “We could use it to get ahead of Eels.”

“And then what?” I say. “Violet, we don’t have a plan for this part.”

“Something tells me my mum and dad didn’t have much of a plan either. But we have to stop Eels from getting the egg, or their sacrifice will have been for nothing.”

I groan. She always has an answer I can’t argue against. An image of Mrs Fossil’s cosy shop interior comes into my mind, complete with buttered scones and sweet tea, but I shake it away.

“Come on then,” I sigh.

“Thank you for coming with me, Herbie.”

“Yeah, whatever,” I say. “Just lead the way before we’re eaten alive by starfish or something.”

Violet ties her torch onto one of her coat buttons. With both her hands free, she begins her descent. I take out my own torch and do the same. Then I follow her down.

The iron rungs are freezing to the touch and my sense of claustrophobia grows sharper still as we climb down the metal tube. There’s a place where the iron is corroded to nothing, and I have to reach down beyond it with my foot to find the next secure rung. Inside the hole made by the corrosion, an octopus – vivid red-orange – slaps one tentacle against the wall, and fixes me with a watery black eye.

“Please tell me we’re nearly there,” I gasp down the tube to Vi.”

“Just a bit further,” she says.

And then my foot is dangling. I’ve reached the bottom rung, and I splash down into a corridor as quietly as I can.

We’re deep in the ship now, at the waterline. Our feet are submerged in the bone-freezing sea, and I curse the fact that no one in the Grand Nautilus Hotel has ever lost a pair of wellington boots, size six and with a nice fuzzy lining.