Kim was thankful that the police had arrived when they did, because the sound of her front door being broken down had briefly distracted Shirley, meaning Kim was able to turn her face as the bottle came down, so it hit her shoulder. The bottle had broken, and she had splinters of glass in her skin as well as a deep cut, but it could have been much worse. Shirley had been handcuffed and taken away while two officers had waited with Kim for an ambulance to arrive. The gash on her shoulder needed stitches.

Palmer and Barrett sat in the interview room waiting for Shirley to be brought in. She had already been arrested for murder and, with the evidence they’d discovered on Janet’s iCloud account, both men were confident she would be charged later on that day. The interview was a formality.

When Shirley appeared and sat down opposite them, she folded her arms across her chest and fixed Barrett with an icy stare.

‘Mrs Grubb.’ Barrett leant his elbow on the table and rested his chin in his hand. ‘I think it would be much better for you if you cooperated with us. You are facing a double murder charge, along with one of attempted murder. These are very serious offences and you are likely to be looking at a life sentence. This is your chance to tell us what happened.’

Shirley shifted in her seat and looked across at her solicitor, who gave a small nod of his head.

‘What’s the point?’ She shrugged. ‘You think you know it all. Nothing I say is going to change that.’

‘You are aware that we have video footage of you killing Toni Jones on Stourbridge Common, on the evening of June twenty-first?’

Shirley’s eyes bulged with disbelief. She clearly had no idea such evidence existed.

‘What? How?’

‘It was retrieved from the mobile phone account belonging to Janet Cox. It appears Ms Cox had been filming you for months.’

Shirley hung her head and let out a long, loud sigh.

‘Stupid bitch.’

The solicitor gave an uncomfortable cough.

‘So, you see,’ Palmer said, ‘it really would be better if you just explained everything, in your own words.’

Shirley lifted her head and stared coldly at Palmer. This was his first encounter with a female killer who had not acted in self-defence, and he felt his blood run cold.