“How did it get in?” I say. “The, er, ‘intruder’, I mean. All the other windows seem intact.”

“They are,” says the doctor. “But can you smell something unusual, Herbie Lemon? Something that will give you a clue?”

I sniff. The place smells of beeswax polish and ancient wood and preserving fluid and old, old stone. And something else.

“Soot?” says Vi, also sniffing.

Together we turn to a huge medieval fireplace that reaches up one of the walls, deep enough to stand in.

“It doesn’t look like a fire has been lit in here for years,” says Vi, as we step inside and look up. Far above, a rectangle of cold night sky is visible, a single shimmering star winking in the centre.

“Not for centuries,” agrees Dr Thalassi. “And yet look down.”

We do so. There are newly fallen flakes of blackened stone and brick on the hearthstones.

“It came down the chimney,” I say, looking back up again.

“Someone did, at least,” says the doc.

“Wait, what’s that?” says Vi, pointing up the chimney. The doctor lifts the lantern and something gleams, stuck between two stones. The doctor plucks it out. He holds it to the lantern, and we gather round the object in his fingertips.

It’s a scale – rigid and sharp and iridescent with purples and greens.

And big.

“Evidence?” says Violet, glancing at the doctor.

“Hmm,” he says, slipping the scale into his waistcoat pocket.

Fixing a piece of board over the broken window takes less time than I expected. With the doctor up the ladder and me passing the nails, Violet has nothing to do but hold the doc’s dressing gown while she waits for us to finish.

Dr Thalassi insists on walking us back to the hotel. But I’m a bit nervous – I’m still keeping Violet a secret, remember? – and I manage to persuade him to leave us at the corner of Spindrift Alley, a little way from the hotel entrance. We watch as he strolls back up to his museum, swinging his umbrella. He lifts his astrakhan hat to say goodbye and then he’s gone.

Back in the hotel, I’m disappointed to see that Amber Griss is still on duty at Reception, which means she, at least, knows how late I got back. She gives me a wink, which means she probably won’t tell old Mollusc, but I can’t be sure. There is a pile of stuff for me to sort on my cubbyhole desk. I gather it up and vanish down to my cellar, where, of course, the wood burner is now midnight-cold. I open the window and Violet hops down.

“We need to decide what we’re going to do next,” she says, but I hold up my hand.