‘Mrs Locke?’ The sound of his voice brought her back, and she opened her eyes. ‘I know this must be hard for you to process, but we’re coming into this whole thing late on. Whatever happened in that flat looks like it happened a long time ago, so we need you to cast your mind back and tell us absolutely anything you can remember about Natasha. Who were her friends, what hobbies did she have, did she have a boyfriend?’

‘She was such a good girl.’ Mary Locke had a faraway look in her eye, her mind stretching back over thirty years, and her voice was quiet when she spoke. ‘We had our differences but she would never have hurt anyone.’

‘Mrs Locke, I need you to focus for us. Who did she hang around with? Is there anyone you can think of that we can speak to who might have seen her the week you last saw her?’

Mary Locke shook her head. ‘Excuse me for just a minute. I need to get a tissue.’ She stood up and walked quickly through the door and back out into the hall. Porter and Styles  turned and looked at each other. Styles raised his eyebrows, and leant in close to whisper.

‘You know she didn’t need to get a tissue, right?’

Porter nodded. He had spotted the tell-tale lump of the handkerchief just beneath the hem of her sleeve as well. They sat patiently until she returned several minutes later, dabbing at her eyes with a scrunched-up paper hankie. Porter gave her a sympathetic smile as she took her seat again opposite them.

‘I do apologise, Detectives. It’s just come as a bit of a shock that something might have happened to her. I really can’t think of anything that might help, though. I hardly knew any of her friends to speak to back in the day, let alone where they are now.’

‘What school did she go to?’ asked Styles.

‘St Agnes’ Catholic School. It’s near where we used to live, when I was still with her father, that is.’ She pulled at the tissue as she spoke, tearing it in several places and winding the strands around her fingers. Styles jotted the name down. They could speak to the school and get details of who else was in her year.

‘If only she had …’ Her voice trailed off as the crunching of gravel outside was accompanied by the low growl of an engine.

‘If only she had what, Mrs Locke?’ asked Porter.

She craned her neck to look out of the window as a sleek black car swung round towards the double garage. The car’s windows were tinted, but Porter thought he saw only one occupant. He looked back at Mary Locke, who seemed not to have heard his question. He repeated it a second time, but she was already on her feet and moving towards the door.