But even as she replied Zoe turned and continued following Hannah down the street. ‘No way, I’m not giving up now. Fuck knows what all that was about, but I’m certain she didn’t look at me once. I’m going to keep following her. I’ll speak to you soon.’ And with that, she hung up.

Swearing loudly, Clara watched as they both disappeared from sight. Frantically she dialled Mac’s number.

He picked up on the first ring. ‘Clara? Thank God. Are you OK? Hold on, I’ll put you on speaker.’

Quickly she told them what had happened. ‘I don’t know what to do! Zoe thinks Hannah didn’t see her, but what the fuck was she doing? Why was she staring at me like that? The expression on her face was just – oh God, I’m really worried, I’ve got a bad feeling about this. I think you should call Zoe, Mac, and tell her to back off, I—’

But Rose’s voice cut through her garbled words. ‘No! Don’t call it off! Please, Clara. Please let Zoe find out where she lives.’

She closed her eyes. The desperation in Rose’s voice was tangible. She heard Tom speak next. ‘Mum’s right,’ he said. ‘It’s our only chance.’

She released a long, pent-up breath. ‘OK,’ she said reluctantly. ‘OK. I’m on my way back now. I’ll see you soon.’

When she returned to Mac’s flat, the air was thick with tension as she took a seat amongst them in the kitchen, four pairs of eyes fastened on her face as she described to them what had happened, recounting every single word and gesture, careful not to leave anything out, beginning from the moment Hannah appeared in front of her and ending with the strange shock of turning to find her standing motionless in the street, watching her.

When she’d finished, an anxious silence hung in the air and they sat staring at Clara’s phone, which she’d placed on the centre of the table, waiting for Zoe’s call. ‘Christ, when will she ring?’ Clara asked shakily.

‘Surely she should have phoned by now?’ Rose asked.

‘Not necessarily,’ said Mac. He looked at Clara and tried to give her a reassuring smile, adding, ‘I’m sure it’ll be soon.’

It was half past eight – an hour and a half since Clara had left Zoe to follow Hannah – when the phone eventually rang. Clara leapt on it, putting it on speaker. ‘Zo?’ she said. ‘Oh thank God, are you OK?’

‘Yes, it’s me,’ she said, her voice breathless and exhilarated above the noise of traffic in the background. ‘I’m fine. I’m on my way back now.’

Clara closed her eyes, relief washing over her. ‘What happened? Where did you follow her to?’