Somewhere in the house I could hear a television set, then silence and the opening of an upstairs door. I had a sense of the house coming together, of it focusing on one common point of attention. Me.

I followed the man, who I assumed was Aamir’s younger brother, into a large open-plan kitchen that was largely Western in décor and awash with floral prints. There was one painting on the wall, of a scene that I thought was probably Mecca, and several framed verses in Islamic calligraphy. Otherwise, only the bookshelves which covered the wall around the fireplace hinted at the Asian ancestry of the room’s occupants. And the occupants themselves, of course.

There were no photographs anywhere.

As I appeared, a man in his fifties rose to meet me. He’d been sitting in a chair by an open fire, reading a newspaper. He folded it carefully and inclined his head before stepping forward and holding out his hand for me to shake.

‘I’m Hassam Chowdhury,’ he told me. ‘Detective Flint, is that right?’

I would hardly have known him for the semi-crazed, grief-stricken man I remembered from the park. This man was traditionally dressed in loose cotton trousers and a long pale-brown tunic. He wore a knitted cardigan in deference to the cold, but it didn’t seem at odds with the rest of the outfit. His hair was cut short, his hairline receding, but there was no grey in his beard. He was tall and well-built, and every movement he made seemed considered and precise.

I heard a sound behind me and turned to see another man enter the room. Early thirties. Traditionally dressed. Bearded. This would be the eldest son. Aamir had been the second son.

‘I’m very sorry for your loss, Mr Chowdhury,’ I said, before turning towards the women in the room. ‘For all your family’s loss.’

The women barely acknowledged me, continuing with their food preparation. I could smell lamb, frying onions and something sharp that was making the insides of my nostrils twitch. The kitchen was a little old-fashioned. Several dozen gleaming copper pans and utensils hanging from the ceiling gave it an exotic appearance, as did the tied bunches of dried herbs interspersed among them.

There were four women. The short, plump lady in her fifties I recognized as Aamir’s mother. Another, who looked much older, was presumably Mrs Chowdhury senior. A woman in her mid twenties was chopping dried apricots, and the youngest, still a schoolgirl, sat at the table, books spread out in front of her.

All four wore traditional Pakistani dress: flowing trousers and embroidered tunics, headscarves that had been allowed to fall loose around their shoulders. I paid particular attention to the two younger women. The one standing might be tall enough to be my woman in black, but I wasn’t sure. She had a thin, proud face and a long, slender nose. Her eyes, when they looked into mine, were black and impossible to read. The younger girl never once looked up.

Mr Chowdhury motioned that I should sit down and I took the armchair on the other side of the fire. All the time he and I were talking, the women carried on with their work. Their movements were slow and quiet. They said nothing to each other. I knew they were aware of every move I made and every word I said.

‘You have something new to tell us?’ Mr Chowdhury asked.

‘It’s only a small thing, but we thought you would appreciate knowing,’ I said. ‘The masks that were found on Union Street, which we believe were worn by your son’s attackers, have been examined by our forensic experts and we’ve just had the report back. On one of the masks, they found very small traces of DNA.’

The reaction was muted but clear. I sensed the two sons moving behind me. Their father seemed to lean a little closer.

‘Unfortunately, it doesn’t take us much further forward at this stage,’ I went on quickly, because Tulloch had drummed it into me that I must not give them false hope. ‘I don’t know how much you know about DNA, but it doesn’t always give the certain answers that people seem to expect.’

One of the sons said something in Urdu to the other.

‘Meaning?’ asked the father.

‘Because the five men we arrested that night are all known to the police,’ I went on, ‘we have their DNA on record. It’s been standard procedure for some time when people are taken into custody. I’m afraid, though, that we haven’t been able to establish a match between any of them and the DNA we found on the mask. We’re sending it back to be examined again. We may find more a second time. On the other hand, it could have come from someone completely unconnected with the attack. The person who sold the masks, for example.’

Mr Chowdhury nodded his head slowly.

‘The reason we wanted you to know,’ I said, ‘is that if news gets out that we’ve found DNA and not brought any charges, people could get very angry. The general public seem to equate DNA with cast-iron proof. Unfortunately, it’s not always that simple.’

‘I understand,’ he said. ‘Thank you.’

‘There is another reason why I wanted to come here this evening,’ I said. ‘I was in the park the night your son was killed. I live very close by and I was on my way home when I heard the call from our Control room.’

The man visibly stiffened. ‘You were the off-duty police officer we heard about?’

I agreed that I was. ‘I saw your son’s attackers,’ I went on. ‘As far as we know, I’m the only witness of the attack itself and it’s largely my fault that the police don’t have a better description of them. It was dark and it happened very quickly, but I wanted you to know how sorry I am about that.’

‘Your sorrow does not bring my brother back. And it does not compare to ours.’

I turned to face the son who’d spoken. The youngest – and the only one not wearing traditional dress. ‘I know that,’ I said.

‘You put the flames out,’ said the father, and I was glad to turn away from the accusation I could see in his son’s eyes. ‘And you put water on his burning skin. He would have suffered much more had it not been for you.’

For a second the man’s pain shimmered across his face. He almost seemed about to break down again, to scream the way he had in the park. Then it was gone.

‘I’m sorry I couldn’t save him,’ I said. ‘I won’t disturb you any longer.’

I got up and took a card from my pocket. ‘If you need to contact me at any time,’ I said, leaving it on the table. I avoided looking at any of the women, but I made sure the card was close to the girl doing homework.

‘If you don’t mind my asking,’ I said, just before I left the room, ‘was your son engaged to be married?’

All movement in the kitchen stopped.

‘Why do you ask?’ said Mr Chowdhury.

‘I know he didn’t live here with you,’ I said, ‘and I understand that’s quite unusual in your culture. I just wondered if he was preparing to be married.’

‘My son was a doctor at St Thomas’s,’ he replied. ‘He worked on call and had to be within a twenty-minute journey of the hospital. He used to say that it made very little difference, that my wife and my daughters were round at his flat so much that it never really felt as though he’d moved out.’

I risked a smile, and saw it returned. He made a strange, old-fashioned, Eastern gesture. I’d never seen it before, but it had the feel of a blessing about it. As I left, I turned to the mother one last time. She met my eyes with her large, brown ones and I had a feeling that however long I stood there, she would continue looking back.

‘I don’t know, Ma’am,’ I said over the phone to Tulloch a few seconds later. ‘I left a card behind so they can contact me if they choose, but you were right, it probably was a waste of time.’

‘Probably,’ she agreed. ‘There was something I should have mentioned before, but I just didn’t think of it. I tried to call you back, but you must have put your phone on silent.’

I pulled my phone out. Sure enough, one missed call from Tulloch.