Lolly and Craig showed their warrant cards. ‘Detective Constables Chambers and Power.’

‘I’m Jon Wilson, one of the counsellors here.’ The man examined their identification carefully and handed it back. ‘You’re lucky I’m in so early.’

‘What is it you do here, exactly?’ asked Craig as they walked into what looked like a residential flat converted into a public space. He looked around the room with its dirty dado rail, cornices and ceiling rose, the jumble of plastic chairs, and the walls filled with public health posters about drug and alcohol abuse, mental health issues and STDs.

‘We try to help people who identify as having a drug problem,’ said Jon. ‘We assess them for treatment, arrange for substitute medications and rehabilitation, and we provide practical support.’ He sprayed the handle of a door with the cleaner, rubbed it with the cloth. ‘And, of course, people with drug dependencies can have somewhat disordered lives so we give them advice about employment and family and law issues. Basically,’ he said, ‘we help in any way we can.’

‘That’s really cool.’ Lolly nodded at the chairs placed in a broken circle around the bare room. ‘And you have group therapy sessions here?’

‘We do small groups. It can be useful for addicts to learn from each other’s experiences and problems.’ He looked at them both. ‘What is it I can help you with?’

‘A woman called Lydia Tide came here,’ said Craig.

‘Why, yes, we know Lydia.’ Jon hesitated. ‘Has something happened?’

‘She’s dead,’ said Craig with a bluntness that made Lolly wince.

‘That’s terrible, how did she…’

‘She may have overdosed.’

‘Wow, okay.’ The man looked shocked. ‘I really liked Lydia, she was a funny lady.’

Lolly felt for him. ‘I’m really sorry.’

‘As you can imagine, we’re no strangers to death around here. The lifespan of addicts can be appreciably lower than for the general population, but that’s really knocked me for six. I thought Lydia was clean…’

‘We’re waiting on the post-mortem result,’ said Craig.

Jon sighed and started moving around the room again, briskly squirting the top of a chair and pulling the cloth along it. ‘So what is it I can do for you?’

‘Lydia had been seeing someone in the last few weeks,’ said Lolly, ‘a fella she met in one of your group sessions.’

‘I don’t know anything about that.’

‘We’re keen to talk to him. His name is Matt, or Matthew, Foster. That’s what she called him, anyway.’

They heard the front door open downstairs. Jon nodded to a small office behind the main room.

‘We should talk in private.’ He stepped aside as Craig and Lolly went in. ‘I’m afraid I can’t just give out details of our clients like that.’

‘Clients?’ Craig laughed. ‘That’s what you call them?’

‘Well, yes, that’s exactly what they are.’ He smiled. ‘What would you prefer we called them?’