“—it’s the River, which perfectly well lets you say, Imagine the River—”

“Mercy, either you don’t like my previous, perfectly good river phrasing, or you do. Pick one.”

“I will not help you to make hyperpotamous travel happen, thank you for the option, my lord,” said Mercy.

“In that case, despite hyperpotamous being a perfectly good word that both catches the ear and does what it says on the tin, let’s deviate,” said the Lord of the Nine Houses, who apparently existed within a complex power dynamic. “I’ll use Cassiopeia’s.” (“Oh, no, the lava,” said Mercy.) “Girls, imagine a rocky planet with a magma core beneath the mantle.

“Travelling overland from point to point might take a year. If you understood your journey and the relative spaces well enough, you could instead drop into the magma, which would carry you to your destination in an hour.”

He paused. The inside of the shuttle seemed very silent to you; there was no sound from its internal apparatus, excepting an occasional huge creak from its rudder mechanism. Ianthe’s voice broke this mechanical, cold-steel silence by saying, quite carefully for Ianthe: “Teacher, the River is an enormous liminal space formed from spirit magic, populated with ghosts gone mad from hunger.”

“The magma metaphor falls apart from here,” said Mercy, eyes still on the pilot’s switches.

The Emperor responded with perfect gravitas: “Let us imagine the magma is full of unkillable man-eating magma fish. Two problems arise. The first is that beings made of flesh and blood immediately die in magma. The second is our vulnerability to man-eating fish.”

Your tolerance for man-eating magma fish would have been tested sorely by anyone who was not God. His divinity earned God, you thought, about sixty more seconds. But then he said, more quietly: “We are about to travel forty billion light years, to where we first ran … myself, and my remaining six. One of our number was dead already, and another had been removed from play. We needed somewhere to lick our wounds, somewhere far away from anything we loved, to wait—to disperse—without fear that the eyes turning upon us would plough straight through the Nine Houses as they went. It’s a dark and cold and unlovely part of space, and the stars there are old and were nearly dead then. We nuked them with thanergy and now they’ll shine forever, but the light is not the same … It would take us years to get there if we went from stele to stele. How far away from the system was Number Seven at last reckoning, Mercy?”

“Counting down, five years,” said Mercymorn, whose hands had at last stilled on the board of buttons and switches and enamelled bone. “Five years, six months, one week, two days.”