The sounds of Louise vomiting were loud enough that Hanson could hear them from the foot of the stairs. Hanson hesitated for a moment, and then went to the kitchen and pulled open the cupboards until she’d found a pint glass. She ran the tap cold, filled it, and then quietly moved upstairs.

There were still isolated noises of retching going on, but it sounded as though there was little coming up now. Hanson followed the sounds into a large double bedroom at the front of the house, where she had a view through into an en suite. She could just see Louise’s feet, soft and grey in her boots where they rested on the tiles. She was clearly kneeling over the toilet.

The human side of Hanson was both sympathetic and hesitant. She wasn’t entirely sure Louise would want a police officer intruding while she was being ill, but she wanted to offer help in case it was needed.

And then there was the copper in her, which was alert to everything else. It was taking in the details of how Louise lived, from the perfectly made-up bed to the spotless surfaces. From the severe Scandinavian colours to the obvious high quality of everything she was looking at.

It was the copper in her that picked up on the one small imperfection. The tiniest spot of dark red on a pale grey carpet, just under the edge of the large double bed.

Hanson paused momentarily between one step and the next. Her mind went through the options. It might be nail varnish. Coffee. Some flaw in the carpet.

But Hanson had learned enough of Louise to doubt it. She was clearly obsessive about tidiness and order, and it seemed impossible that she would have let a mark spoil that carpet.

Hanson could see more of Louise now. She was facing almost entirely away from Hanson, slumped on her arms, which were folded across the toilet seat. The picture of misery.

Hanson was only too happy to use that misery to her advantage. She moved over to the bed, and then crouched. Close up, the spot on the carpet was rusty red, and Hanson felt a shiver run through her. It looked very much like dried blood.

She ran her eyes along the bottom edge of the bed, which was a pale grey velvet. And then, glancing towards the bathroom again, she put a hand out to a point just above the stain on the carpet and lifted the very edge of the sheet.

It took one glance to tell her everything she needed to know, and she felt dizzy as she tucked it in again and got back to her feet.

She took another two steps towards the bathroom, and Louise turned, her eyes bloodshot and her expression stricken.

‘Have some of this,’ Hanson said, gently, and handed her the water.