And then someone screamed. It could have been Maryam. It could have been Zahra. Now that her senses had begun to gather, she could see clearly that the object in the man’s hand was a knife. At that moment, he lunged towards one of the passengers. An arc of something sloppy and dark flew up in the air and someone screamed again.

For a moment there was just the rushing of blood pumping around Zahra’s skull. She experienced a floating sensation, as if she was looking down on herself, clawing at the buckle and restraint. And then the true horror of what was happening in the carriages ahead of her crashed into her mind with a force that robbed her of breath. Her mum, her brothers, her friends, they were in the train in front, and they were trapped by the ride’s safety restraints. And that man was attacking them where they sat, unable to free themselves.

She cried out, breaking the silence and yanking her mind back into her body. Nausea welled in her guts. She tore at the buckle and opened it. But still the restraint wouldn’t budge.

The attendant leant forward again. Zahra couldn’t see who he was attacking, just the backs of their headrests and the very tops of their heads. A pair of hands flew upwards from the seat to push him away, and then, instinctively, their owner held them over their face in a futile gesture of defence. The man slashed the blade at the exposed part of their body under their arms. An animal howl filled Zahra’s ears.

Maryam’s eyes were wide open with terror. ‘Stop him,’ she yelled. Zahra wished she’d had the sense to call out too. The queue of passengers didn’t seem to have moved and the woman in the cabin was still in her seat. Couldn’t they see what was going on?

The man in the emerald shirt continued to move in slow motion. He stooped in front of the next car and again a hand reached out, fingers splayed, clearly the desperate attempt to stop him. But the hand met the knife and there was another jet of blood and, with it, a chunk of something fleshy.

Zahra’s heart pounded. Sweat was trickling down her back and her head was hot. And still the man kept moving down the train in front. Was that her mum? The train was too far away for her to see clearly, and her vision was blurred with the sweat she kept desperately trying to blink away. But it was a woman’s arm that had shot up and, for a second, she caught a chilling glimpse of her mother’s hijab.

Zahra cried out again, and then, finally, there was movement in the queue of people waiting in the stalls. A bald, middle-aged man yelled at his family to stand back, then dodged under the wooden barrier and picked up the pole the attendant had been using minutes before to check the height of the children on the ride.