And Mardina had left behind Monica Trant, on the wrong side of the ISF officers.

Mardina tried to get back to her. ‘Oh, hell, Monica, this is my fault, I slowed you down—’

‘It doesn’t matter. I’ll be fine. Stay safe.’ The lock door was already swinging closed, and Trant had to duck to maintain eye contact with Mardina. ‘And listen, if you get the chance, tell my son Rob that—’

The hatch clicked closed. The ISF officers, sweating, breathing hard, glanced at each other and backed away.

‘Hell of a thing,’ said the woman to the man.

‘Too damn right.’ The man turned and raised his voice to address the passengers. ‘Please find a couch. If you can’t find a couch, wedge yourself in somewhere, we are over capacity. We lift immediately.’ He and his colleague made for the rear of the cabin, near the hatch to the corridor, and folded couches out of the wall.

Mardina, bereft, bewildered by the sudden transition from the crowded space to the interior of this craft, pushed her way in. She had ridden these bugs many times. They were just hoppers that took you from dome to dome, squirting their way over Mercury’s surface on feeble chemical-propellant rockets. You rode them at shift changes, at dome-morning or dome-night, when going to see a colleague, or travelling from a dormitory block to a workplace. Now the interior of the bus, with its curving walls and soothing beige colour scheme, had never seemed so small, so crowded was it with people, all scrambling to get to the few remaining couches. You weren’t meant to be fleeing for your life in a vessel like this.

Mardina found a place by the wall, next to a couch where a young woman cradled her baby, and sat on the carpeted floor with her feet jammed against a strut.

She had barely settled when the bug lifted with a lurch, much more roughly than she remembered from any early morning commute. People gasped or called out; a few who weren’t safely strapped into couches stumbled and fell to the floor. A baby started crying. And the lift went on and on, not like a commute hop, this was a single mighty leap which would, when the fuel was exhausted, fling them away from Mercury altogether – where they would drift in space until picked up, if they ever were.

Mardina wondered how long was left until the impact of the Nail.

And she thought about the kernels.

She knew that kernels were like tiny wormholes, leaking energy, that could be manipulated open and closed with lasers and magnetic fields. Had anybody done any modelling of what might become of the kernels, and the energy they channelled, when the Nail was driven into the Mercury ground? Presumably the Chinese couldn’t have; they were supposed to have no access to kernel physics anyhow. Maybe they thought this was just a surgical strike. Closing the lid of the UN’s treasure trove: nothing more destructive than that. But if not . . .

Mardina still had her slate, in its pouch at her waist. As the clumsy craft’s acceleration juddered on, as the passengers gradually quietened down, she dug out the slate, and looked up at the woman with the baby. ‘Excuse me. Can I use your comms link? The one on your couch . . .’

The woman shrugged, holding her baby’s head against her chest.

Mardina pulled down a small earpiece on a fibre-optic cable from the couch. She swiped it with her slate to give it her ID. The earpiece lit up, and she tucked it behind her ear. ‘I want to speak to my daughter. Beth Eden Jones.’ She swiped another ID, to identify Beth. ‘I know she’s on a hulk ship heading towards the outer system. I’ll record a message. I want you to keep trying to make the call until you get a response, right?’

‘Confirmed,’ replied a soft synthetic voice.

So the solar system’s shared comms systems were still working, at least. She looked around, self-conscious. Nobody was paying any attention to her, but she ducked her head even so. ‘Hi, sweetheart, it’s your mother. You won’t believe where I am . . .’

There was a streak of brilliant light, beyond the cabin walls, quite soundless, like a meteor falling. People turned, distracted.

Still the bug ascended from Mercury, as smoothly as before.

‘If I get a chance I’ll tell you all about it. But the main thing is, I’m sorry I had to throw you at General Lex, even if he does owe me a favour. Wherever you end up I’ll come looking for you. Don’t forget that I’ll always

CHAPTER 85

Monitors in space and elsewhere observed the event, reconstructed its consequences later, and reported their conclusions to survivors. Or attempted to.

The Nail hit the surface of Mercury, dead on target at the kernel-physics facility at Caloris, at one per cent of the speed of light.

It delivered the kinetic energy of an asteroid three hundred metres across moving at interplanetary speeds. An energy load equivalent to all of Earth’s nuclear arsenals at the most dangerous moment of the twentieth-century Cold War. An energy load equivalent to a month of the planet’s entire output, in the most profligate days of the twenty-first century. All of this energy was injected into the upper crust of Mercury, and the kernel beds beneath, in less than a millisecond.

The kernel facility, with a wide swathe of the crust, was utterly destroyed, rock vaporised to gas. The molten walls of a tremendous new crater rolled across this world’s battered surface.

But the Nail’s fall was only the trigger. In response to the tremendous shock, in layers deep beneath the surface, kernels yawned open, like the mouths of baby birds. And a pulse of energy of an intensity never before seen in the solar system was unleashed, carried by a flood of short-wavelength photons, X-rays and gamma rays that fled the site at the speed of light, and then by a wavefront of massive particles, moving somewhat more slowly, but highly energetic themselves.

After a fiftieth of a second the radiation pulse had passed through the body of Mercury. Across the face of the planet the rocky crust was liquefied, the human installations on the Mercury ground gone in a moment. Even the iron core roiled.

After another fiftieth of a second the photon wave overwhelmed the fleeing surface-hopper bug, and the rest of the armada of fragile refugee ships, rising from the surface. To Mardina it was as if a light went off inside her head, inside her very skull.

After eight minutes the photon shockwave reached Earth.

CHAPTER 86

Officer Rob Trant was on duty, cruising the east side of New Prudhoe, Alaska.

He was well aware of the date, and the time. This was when the Nail was due to strike Mercury, as his mother Monica had warned him. But despite having this inside channel he didn’t know much more about the international crisis than any other cop in the country.

They’d been briefed about fears of a backlash on Earth, whatever happened up in space: a rising by ethnic Chinese types in the cities, maybe, or some kind of revenge attacks taking place on them in turn. Whatever. Rob had seen nothing untoward so far, in the ruined suburbs he patrolled. But he knew the news of even the most dramatic events on Mercury would take long minutes to crawl out here at lightspeed.

Personally he didn’t think anything would come of it. The whole Chinese winter thing had been a kind of bluff, after all.

He knew his mother was in the centre of it, on Mercury he could never have persuaded her to come away. She had opened up to him more in recent days than for a long time, in fact more than since the moment he’d finally rebelled at his life under a dome on Mercury, and had cashed in his partially completed ISF training to become a cop on Earth. It was hard to have a decent conversation with the long minutes of light delay between the worlds. She’d promised him some kind of message today, a long missive. But the message hadn’t come, not yet.