The next day Zanna and Deeba wandered through the playground, watching their reflections in all the puddles. Bedraggled rubbish[17] lurked by walls. The clouds still looked heavy.

“My dad hates umbrellas,” said Deeba, swinging her own. “When it rains he always says the same thing. ‘I do not believe the presence of moisture in the air is sufficient reason to overturn society’s usual sensible taboo against wielding spiked clubs at eye level.’ ”

From the edge of the playground, near where the respectful fox had stood, they could see over the school’s walls, into the street, where a few people passed by.

Something caught Zanna’s eye. Something strange and unclear. By a playing field at the end of the street, smudges were just visible on the road.

“There’s something there,” said Zanna. She squinted. “I think it’s moving.”

“Is it?” said Deeba.

The sky seemed unnaturally flat, as if a huge gray sheet had been pegged out from horizon to horizon above them. The air was still. Very faint dark stains coiled and disappeared, and the road was unmarked again.

“Today…” Deeba said. “It’s not a normal day.”

Zanna shook her head.

Birds arced, and clutch of sparrows flew out of nowhere and circled Zanna’s head in a twittering halo.

That afternoon they had French. Zanna and Deeba were not paying attention, were staring out of the windows, drawing foxes and sparrows and rain clouds, until something in Miss Williams’s droning made Zanna look up.

“…choisir…” she heard. “…je choisis, tu choisis…”

“What’s she on about?” whispered Deeba.

“Nous allons choisir…” Miss Williams said. “Vous avez choisi.”

“Miss? Miss?” said Zanna. “What was that last one, Miss? What does it mean?”

Miss Williams poked the board.

“This one?” she said. “Vous avez choisi. Vous: you plural. Avez: have. Choisi: chosen.”

Choisi. Shwazzy. Chosen.

At the end of the day, Deeba and Zanna stood by the school gate and looked out at where they had seen the marks. It was still drizzling, and by the playing fields, the rain looked to be falling as if against resistance, as if it had hit a patch of odd air.

“You coming to Rose’s?” Kath and the others were standing behind them.

“We…thought we saw something,” Deeba said. “We was just going to…”

Her voice petered out, and she followed Zanna. Behind them, a scrum[20] of their classmates were rushing by, heading home or meeting their parents.

“What you looking for?” said Keisha. She and Kath stood watching quizzically as Zanna stood in the middle of the road a few meters away, and looked around.

“I can’t see nothing,” she whispered. Zanna stood for a long time, as the others huffed impatiently. “Alright then,” she said, raising her voice. Kath had her arms folded and one eyebrow raised. “Let’s go.”

The stream of their classmates had ended. A few cars emerged from the gates and swept past them as their teachers headed home. The little group of girls were alone in the street. With a sputtering crack, the streetlights came on as the sky darkened.

Rain was coming down hard like a typewriter on Deeba’s umbrella.

“…don’t know what she’s doing…” Deeba heard Becks saying to Keisha and Kath. Zanna walked a little ahead of them, her feet sending up little sprays of rainlike mist.

A lot like mist, a dark mist. Zanna slowed. She and Deeba looked down.

“What now?” said Keisha in exasperation.

At their feet, a few centimeters above the dirty wet tarmac, there was a layer of coiling smoke.

“What…is that?” said Kath.

Wafts were rising from the gutters. The smoke was a horrible dirty dark. It emerged in drifts and tendrils, reaching through the metal grilles of the drains like growing vines or octopus legs. Ropes of it tangled and thickened. They coiled around the wheels of vehicles and under their engines.

“What’s going on?” whispered Keisha. Smoke was beginning to boil out of the sewers. A smell of chemicals and rot thickened in the air. Far off and muffled as if by a curtain, the noise of a motor was audible.

Zanna was standing with her arms out, focusing intensely into sudden fumes that circled them. For a second, it looked as if the rain that was pelting them was evaporating, like drops on hot metal, a few millimeters above Zanna’s head. Deeba stared, but dark drifts hid her friend.

The motor was louder. A car was approaching.

The girls were shrouded in gritty smoke. They spluttered in panic and tried to call to each other. They could see almost nothing.

The noise of the motor grew, and glints of reflected streetlamp-light winked momentarily through the fumes.

“Wait a minute,” Zanna shouted.

Through the fog headlights suddenly flared, heading straight for Zanna. Deeba saw her, turned in to a shadow, sidestepping neatly as the lights bore down, her hands seeming to glow.

“It’s my dad !” Zanna shouted, and moved fast as the car raced into the smoke, and there was a rush as the fumes dissipated and—

— there was a bang, and something went flying, and there was silence.

The clouds undarkened and the rain stopped. The strange fumes dropped out of the air and flooded like thick dark water back into the gutters, gushing soundlessly out of sight.

For several seconds, no one moved.

A car was skewed across the road, with Zanna’s dad sitting in the front seat looking confused. Someone was shouting hysterically. Someone fair was lying by a wall.

“Zanna!” Deeba shouted, but Zanna was beside her. It was Becks who had been hit, and who lay motionless.

“We have to get a doctor,” said Zanna, pulling out her mobile[14] and starting to cry, but Kath was already through to 999.

Zanna’s dad staggered out of the car, coughing.

“What…what…?” he said. “I was…what happened?” He saw Becks. “Oh my God!” He dropped to his knees beside her. “What did I do?” he kept saying.

“I’ve called an ambulance,” Kath said, but he wasn’t listening. Now the light was back to normal and there was no fog lapping at ankle-height, people were peering out of doors and windows. Becks moved uneasily, and made groggy moaning noises.

“What happened?” Zanna’s dad kept asking them. None of them knew what to say. “I don’t remember anything,” he said, “I just woke up and—”

“It hurts…” Becks wailed.

“Did you see?” Zanna whispered to Deeba. Her voice sounded as if it were cracking. “The smoke, the car, everything? It was all thick around me. It was trying to get me. ”