Siobhan suppressed a sigh. “Mother, I’m the Astronomer Royal, and this is the Royal Society. I’m making the keynote speech! ‘Technical guff’ is expected.”

“And you never were very good at analogies, dear.”

“You could be a bit supportive.” She sipped her coffee, taking care not to spill a drop on her best suit. “I mean, look where your little girl is today.” She flicked on her phone’s vision options so her mother could see.

These were the City of London Rooms in the Royal Society’s offices in Carlton Terrace. She was immersed in rich antiquity, with chandeliers overhead and a marble fireplace at her side.

“What a lovely room,” Maria murmured. “You know, we have a lot to thank the Victorians for.”

“The Royal Society is a lot older than the Victorians—”

“There are no chandeliers here, I can tell you,” Maria said. “Nothing but smelly old people, myself included.”

“That’s demographics for you.”

Maria was in Guy’s Hospital, close to London Bridge, only a few hundred meters from Carlton Terrace. She was waiting for an appointment concerning her skin cancers. For people who had grown old under a porous sky it was a common complaint, and Maria was having to queue.

Siobhan heard raised voices in the background. “Is there a problem?”

“A ruckus at the drinks machine,” Maria said. “Somebody’s credit-chip implant has been rejected. People are a bit excitable generally. It’s a funny sort of day, isn’t it? Something to do with the odd sky, maybe.”

Siobhan glanced around. “It’s not much calmer here.” As the start of the conference had approached, she had been grateful to be left alone with her coffee and a chance to run through her notes, even if she had felt duty-bound to call her mother at Guy’s. But now everybody seemed to be crowding at the window, peering out at the odd sky. It was an amusing sight, she supposed, a clutch of internationally renowned scientists jostling like little kids trying to glimpse a pop star. But what were they looking at?

“Mother—what ‘odd sky’?”

Maria replied caustically, “Maybe you should go take a look yourself. You are the Astronomer Royal, and—” The phone connection fizzed and cut out.

Siobhan was briefly baffled; that never happened. “Aristotle, redial, please.”

“Yes, Siobhan.”

Her mother’s voice returned after a couple of seconds. “Hello? …”

“I’m here,” Siobhan said. “Mother, professional astronomers don’t do much stargazing nowadays.” Especially not a cosmologist like Siobhan, whose concern was with the universe on the vastest scales of space and time, not the handful of dull objects that could be seen with the naked eye.

“But even you must have noticed the aurora this morning.”

Of course she had. In midsummer Siobhan always rose about six, to get in her daily quota of jogging around Hyde Park before the heat of the day became unbearable. This morning, even though the sun had long been above the horizon, she had seen that subtle wash of crimson and green in the northern sky—clearly three-dimensional, bright curtains and streamers of it, an immense structure of magnetism and plasma towering above the Earth.

Maria said, “An aurora is something to do with the sun, isn’t it?”

“Yes. Flares, the solar wind.” To her shame, Siobhan found she wasn’t even sure if the sun was near the maximum of its cycle right now. Some Astronomer Royal she was proving to be.

Anyhow, though the aurora was undeniably a spectacular sight, and it was very unusual to be so bright as far south as London, Siobhan knew it was nothing but a second-order effect of the interaction of solar plasma with the Earth’s magnetic field, and therefore not particularly interesting. She had continued her jogging, not at all motivated to join the rows of slack-jawed dog walkers staring at the sky. And she certainly wasn’t sorry she missed the brief panic as people had assailed the emergency services with pointless calls, imagining London was on fire.

Everybody was still at the window. It was all a bit strange, she conceded.

She set aside her coffee and, phone in hand, walked up to the window. She couldn’t see much past the shoulders of jostling cosmologists: a glimpse of green from the park, a washed-out blue sky. The window was sealed shut to allow the air-conditioning to work, but she thought she could hear a lot of traffic noise: the blaring of horns, sirens.

Toby Pitt spotted her at the back of the pack. A big, affable bear of a man with a strangulated Home Counties accent, Toby worked for the Royal Society; he was the manager of the conference today. “Siobhan! I won’t make jokes about the Astronomer Royal being the last to show any interest in the sky.”

She showed him her phone. “No need. My mother’s already been there.”

“It’s quite a view, though. Come and see.” He extended his massive arm around her shoulders and, with a skillful combination of physical presence and smiling tact, managed to shepherd her through the crowd to the window.

The City of London Rooms had a fine view of the Mall, and of St. James’ Park beyond. The grass of the park glowed lurid green, no longer a native specimen but a tough, thick-leaved drought-resistant breed imported from southern Texas, and the relentless sprinklers sent sprays of water shimmering into the air.

But the traffic in the Mall was jammed. The smart cars had calmly packed themselves up in an optimal queuing pattern, but their frustrated drivers were pounding at their horns, and heat haze rose in a shimmer in the humid air. Looking up the road Siobhan saw that the traffic control lights and lane guides were blinking, apparently at random: no wonder the traffic was snarled.

She looked up. The sun, riding high, flooded the cloudless air with light. Even so, when she shielded her eyes she could still make out a tracery of auroral bands in the sky. She became aware of a noise beyond the blare of the traffic in the Mall, a softer din, muffled by the thick sealed window. It was a growl of frustrated driving that seemed to be rising from across the city. This snarl-up wasn’t local, then.

For the first time that day she felt a flicker of unease. She thought of her daughter, Perdita, at college today. Perdita, twenty years old, was a sensible young adult. But still …

There was a new silence, a shift in the light. People stirred, perturbed. Glancing over her shoulder Siobhan saw that the room lights had failed. That subtle change in the ambient noise must mean the air-conditioning had packed up, too.

Toby Pitt spoke quickly into a phone. Then he held up his hands and announced, “Nothing to worry about, ladies and gentlemen. It isn’t just us; the whole of this part of London seems to be suffering something of a brownout. But we have a backup generator that should be coming online soon.” He winked at Siobhan and said softly, “If we can persuade the ratty old thing to start up in the first place.” But he raised his phone to his ear again, and concern creased his face.

In the heat of the June day, thirty-plus degrees Celsius, the room was already warming up, and Siobhan’s trouser suit was starting to feel heavy and uncomfortable.

From beyond the window there was a crumpling noise, a series of pops, like small fireworks, and a din of wailing car alarms. The cosmologists gasped, a collective impulse. Siobhan pushed forward to see.

That queue of traffic on the Mall was just as stationary as before. But the cars had lurched forward, each smashing into the one in front like a gruesome Newton’s cradle. People were getting out of their vehicles; some of them looked hurt. Suddenly the jam had turned from an orderly inconvenience into a minor disaster of crumpled metal, leaking lubricants, and scattered injuries. There was no sign of police or ambulances.

Siobhan was baffled. She had literally never seen anything like it. All cars nowadays were individually smart. They took data and instructions from traffic control systems and navigational satellites, and were able to avoid cars, pedestrians, and other obstacles in their immediate surroundings. Crashes were virtually unheard of, and traffic deaths had dwindled to a minimum. But the scene below was reminiscent of the motorway pileups that had still blighted Britain during her childhood in the 1990s. Was it possible that all the cars’ electronic guidance systems had failed at once?