Sara hadn’t seen the house in daylight before; the double-fronted, lead-windowed, dark brick houses set in their calm, tree-lined backwater spoke of a traditional English bourgeois affluence when the very idea of living the other side of the river would have appalled its well-heeled residents. She wondered what Lady Morahan might have made of her husband trekking to the far reaches of south London to meet a young Pakistani woman wearing a hijab.

She rang the front doorbell and looked around. Thirty or so yards up the road, a police car was parked on a double yellow line, inside it a uniformed man and woman.

The door opened, revealing a Lady Morahan whose composure seemed to Sara remarkable. Her night must have been agonising, yet she was smartly dressed in black trousers and a red shirt, make-up concealing any sign of distress, offering a quick smile.

‘Miss Shah, how kind of you to come.’

‘It’s no trouble at all, Lady Morahan.’ Sara cast a glance up the street.

‘Yes, they’ve called in,’ said Iona, following her eyes. ‘Pleasant young man and woman. Said they’re here to keep an eye on things just in case.’

‘In case of what?’ Sara asked, instantly realising what a stupid question it was.

Iona shot her a beady look. ‘Come on, in you come,’ she said briskly. ‘Shall we dispense with “Miss” and “Lady”? I’m Iona, you’re Sara. All right with you?’

‘Of course,’ smiled Sara.

‘Coffee?’

‘Thank you. Only if it’s no trouble.’

‘Not at all. Why don’t you go into the drawing room? Make yourself comfortable.’

The large square room smelt of polished walnut side tables and the residue of dying embers in the fireplace. Above the mantelpiece hung a large portrait of a seated woman swathed in shawls drawing a landscape in a sketch book.

Sara surveyed the room, unable to stop herself imagining hiding places. She walked over to a baby grand piano in the corner; a book of Bach preludes was open on the music stand. The closed top was a display of framed family photographs: Francis and Iona ducking confetti as they emerged through a church porch on their wedding day, he in a grey frock coat, she in a white dress, the apogee of English traditionalism; two daughters, the older raven-haired, the younger auburn, at different ages from toddlers’ dresses to child bridesmaids to school uniform and adulthood; the wedding of the younger to a smiling young man with neatly cut fair hair and a sheen of money and breeding; what she thought might be a fortieth wedding anniversary formal portrait of the Morahans. All far removed from a skinny old man with his trousers halfway down his legs.

She heard a rustle in the passage and swiftly moved from the photographs to the portrait.

‘Searching for something?’ asked Iona with that same beadiness.

Sara smiled ruefully. ‘Examining your family, I’m afraid.’