The service was billed as multi-faith and they had been addressed by Muslim, Jewish and Sikh leaders as well as the Dean of Westminster. The colourless voice of the Dean echoed through the Abbey to mark the end of the two-minute silence. There were more prayers, then they rose and trudged out into the drizzle.

Gabriel kept to the back while the PM laid the first wreath at the Abbey’s Innocent Victims’ memorial: a circular slab of stone set in the ground outside the west door, inscribed with a line from Lamentations – Is it nothing to you all you who pass by. The line had puzzled Gabriel when she passed the memorial on the way in. It seemed bitter, challenging and angry – a strange choice, but perhaps more honest than the platitudes found on many memorials, Gabriel thought as she watched the wreaths being placed around the stone.

She caught Tennant’s eye, who smiled thinly and continued talking to the Home Secretary. A quiet voice made her turn.

It was the girl who had lost her family at Chilton Park, Zahra. Gabriel froze inside. The last time she had seen her on that television interview, she had appeared to be still suffering from shock. Gabriel knew enough of the grieving process to foresee that shock would have turned to rage.

‘It’s Zahra, isn’t it?’

The girl nodded.

‘Once again, I’m sorry for your loss.’

The girl nodded again. She looked like she was struggling for words. Gabriel steeled herself for an onslaught. But instead, the voice was quiet and calm. ‘That day, I asked you a question. Do you remember?’

Once again, the image of Isobel Harris came to Gabriel’s mind. Something in her eyes maybe. ‘I remember.’

The girl continued. ‘The liaison woman who came round. She was good. She told me what had happened to the man who killed my mother and brother. I wanted to be pleased he was dead. But it didn’t work out like that.’

The blast of a siren made Gabriel jump. An ambulance flew past, lights flashing, and barged its way through the cars queuing at the lights in Parliament Square.

‘They just kept on coming. The man who murdered them, he was killed. But they came back. At Trafalgar Square. And Leeds. And Wembley. They don’t seem to stop. Each time it doesn’t get better, it gets worse. And you people, the police, the authorities, the politicians,’ she waved a hand towards the group surrounding the mayor, ‘don’t seem to be able to stop them. Maybe you can’t. But they’re feeding off each other, whipping each other into greater evil. And people like her don’t help.’

She nodded in the direction of Lesley Hogarth, who stood next to the red-haired woman, earnestly engaged in conversation with a thin man wearing a turban.

The girl went on. ‘She – and her kind – they feed all this.’ She waved towards the memorial. ‘For their own ends. They encourage it. Sometimes subtle, sometimes so in your face that you don’t believe it. But always for their own ends. So this, the same question. Will we be safe?’