Then he adds, turning now, looking boldly in her eye. “You are pretty. I did not notice it before.”

In answer, she wraps her arms tight around her slender frame.

They resume walking. As they set off, Livia quickly, furtively crouches down to the cigarettes he has discarded and picks them off the ground one by one. She does not offer an explanation.

Thomas does not ask for one.

ф

She tells him later. They are walking single file, Thomas in front, Livia behind, straining to adjust her pace to his slow stumble. Her explanation has no face, therefore: just a voice, measured and even, reciting the facts.

“The name is Roman,” she says. “Livia Orestilla. An empress: Caligula’s wife. She was to marry someone else, but Caligula stole her on her wedding night. Then he divorced her after only a few days.”

“A funny thing to put into your cradle. In lieu of frankincense and myrrh.”

“That’s just what Julius said. Not the words but the sentiment. It was he who told me. About Caligula.”

Stung, Thomas turns around to her, careful to place his eyes on her face, her jacket closed now, swallowing her body.

“It is good that you hate me. I’m dangerous. I have tainted blood.”

He is surprised to see she holds his gaze. Thus far, she has always avoided it. It must be something she brought up with her, from the depth of the mine.

“So you are,” she replies, serious and not. “‘Tainted.’ ‘Dangerous.’ Why is it you think I’m walking three paces at your back?”

It shouldn’t, but it makes Thomas laugh. When they start walking, her steps fall into rhythm with his.

One pace, he thinks. Two paces at the most.

ф

They reach the border at dusk. The transition is gradual but also distinct. On their side, the dipping sun finds the earth rich and brown; trees tall and proud even in hibernation; hollies growing in green vigour. On the other side all growth is stunted, the soil barren, mixed with Soot, the puddles greasy with sin’s residue, the air pregnant with its stink.

The other side. The city. London.

The day has grown colder and snow is in the air. Thomas wonders whether it will fall black, over there. They stop under the shadow of a tree. It is a species Thomas does not recognise, a conifer nearly as broad as it is high, its branches growing sideways and forming a series of platforms, filtering the last of the sun. On the London side, the tree stands black, smeared in Soot, and threadbare in its canopy. He walks up to the trunk and touches the bark. Livia watches him, puzzled.

“What is it?”