She must snap out of it. London, her logical mind told her, remained safe. For well over a decade after 7/7 only one death, that of Lee Rigby, the soldier drummer hacked to death outside Woolwich barracks, had been the result of terrorism. Not just in the city but in Britain itself. Then came the van and knife attacks in central London; the bombing of a pop concert at Manchester Arena, lethally shattering the calm; the reminder that terror had not, and would not, go away.

Compared with other death tolls – road accidents, fires, polluted air – the figures remained, it seemed to Sara, insignificant. The ultimate victims were ordinary Muslims, tainted by association, fearful of hate-fuelled revenge. Yet, unable to shift the strangeness of Morahan’s scrawled letter from her mind, she found herself edgily inspecting the young Asian with the blue rucksack fidgeting in the corner of the underground carriage. When he stepped out of the train at Kennington, she was, despite herself, unable to prevent a flush of relief.

Back on Tooting Broadway, her mood changed. The Islamic Centre and halal butchers stood contentedly alongside trendy brunch cafés with eager central European waitresses and antipodean chefs. In this part of London few wore the full niqab and burka, but there were plenty of hijabis like herself. Some young Muslim women dressed in figure-hugging jeans and short-sleeved shirts; that was not her own choice now, but she never forgot the time when, all too briefly, she had also enjoyed that lifestyle.

She headed up the Broadway and into Webster Road with its terraces of small 1920s bow-fronted houses. A few sagged unloved, rotting window sills and yellowing streaks from overflowing pipes discolouring their whitewashed frontages. But most were spruced-up and clean, often with recently added porches and front doors proudly displaying their panelled multi-coloured glass. Her shrewd father had bought their house three years after she was born, during the heyday of Mrs Thatcher’s right to buy, a nest for the family he’d once hoped to grow.

She had been just eight years old when her mother had died – how distant it seemed. Not old enough truly to know her; or to ask her what she really believed. Would her mother, with the conviction of a convert’s faith, have seeded in her the certainty her father lacked? Whenever Sara occasionally referred to her, her father never seemed to want to engage; the answer was always a platitude. ‘Yes, your mother was always a good woman.’ ‘Always true to God.’ ‘So beautiful.’ ‘I never stopped loving her.’ It was territory he did not want to enter. After her death, the house had become father and daughter’s sanctuary. She never thought of leaving him, whatever the pressures to marry from aunts and cousins. With him to look after, how could she? The truth was that, far from being her burden, he was her excuse.