‘How can we be? We’ve only met once. We had a five-minute conversation.’

‘It was longer than that.’ Mona sipped on her drink as she walked. ‘And anyway, it only takes five seconds to know if someone’s going to be your friend or not. We hit it off. You can’t deny it. There’s a connection between us.’

‘No, there isn’t.’

‘Of course there is.’

Sadie pushed open the door to the octagonal conservatory. It was furnished with rattan chairs and tables and filled with plants, mainly tall potted palms that cast long shadows in the gloom. A thin light came from the living room along with the sound of laughter and the chink of glasses. There was a temporary pause in the music – maybe someone was changing the tape – and then it started up again: the Drifters singing the Sixties hit, ‘Under the Boardwalk’.

Sadie quickly glanced around, making sure they were alone before speaking again. ‘I don’t know what you want from me.’

Mona stepped in behind her and closed the door. She sipped on her drink, keeping her sly eyes on Sadie. ‘Sure you do.’ A smile flickered at the corners of her lips. ‘Hey, I know it’s kind of scary but you can do it.’

‘Do what?’

‘You know what.’

Sadie swallowed hard. ‘I-I don’t,’ she stammered. ‘Tell me what’s going on.’

A frown settled on Mona’s forehead and a look of distrust crossed her face. She paced to the left and the right as if it might be a set-up and the police were lurking in the undergrowth. She poked among the palms and peered into the corners. When she was sure that they were the only two people in the conservatory, she returned to Sadie and said very softly, ‘I’ve done mine and now you have to do yours.’

Sadie forced herself to utter the words. ‘Are you… are you saying that you killed Eddie?’

Mona smiled again, a chilling smile that didn’t quite reach her eyes. ‘A deal’s a deal. You can’t go back on it now. Not after I’ve kept to my side of the bargain.’

Sadie gulped what remained of her wine, still desperately hoping that the girl was bluffing. ‘I don’t believe you. I don’t believe you did anything.’

‘He’s dead, isn’t he?’

‘That doesn’t mean you did it.’

‘Who else?’ Mona whispered.

‘Then prove it,’ Sadie said, still grasping at straws. She had that vile sick feeling in her guts again. It couldn’t be true. It couldn’t. She wanted to grab hold of Mona and shake her like a rag doll. But what if she wasn’t lying? A trembling ran through her bones, a seismic fear that drained the blood from her face.

Mona pursed her lips. ‘What do you want to know?’

Sadie shrugged, struck dumb by terror.

‘The Mansfield estate,’ Mona said. ‘Carlton House, Number 93.’ She gave another of her weird giggles. ‘Eddie wasn’t very house-proud, was he? The place was a real tip, cans everywhere and it stank of fag smoke. You’d think he’d tidy up every now and again. Still, that’s men for you; dirty bastards, all of them.’

Sadie stared, her heart thumping. Mona couldn’t know any of this unless she’d been to the flat. ‘No,’ she muttered, shaking her head. ‘You couldn’t. You —’

‘Oh, come on. It’s not as though you even liked the guy. He was a shit, Sadie, a user. He got what he deserved. It’s pointless to get all sentimental over him now.’

‘You’re crazy!’

Mona’s face took on a hurt expression. ‘Don’t say that. I only did what we agreed.’

‘We didn’t agree anything.’

‘Of course we did. And you can’t go back on your word.’

‘What?’ Sadie felt as if the whole exchange was surreal, a nightmare that she wasn’t able to wake up from. ‘I never promised anything. I didn’t want Eddie dead. Why would I?’

Mona inclined her head and gazed at her for a moment. Eventually a smile slid on to her lips. ‘It’s okay. You’re just scared, right? I get it. But there’s no need. I’ve got it all planned out. You won’t get caught, I promise. It’s foolproof. You won’t even have to go into the house.’

‘No, I won’t. Because I’m not going near it. I’m not having any part of this. Do you understand? I don’t… I don’t want anything more to do with you.’

‘It’s a bit late for that.’

‘I want you to go away and leave me alone.’

Mona sipped on her vodka, leaving a pale pink stain of lipstick on the rim of the glass. ‘I know what you’re thinking,’ she said. ‘As soon as my back’s turned, you’ll go to the cops and tell them what I did.’

‘I won’t,’ Sadie lied. ‘I swear. I promise.’

A malevolent gleam crept into Mona’s eyes. ‘The thing is,’ she said, ‘if you do that then I’ll have to tell them everything: how we met on the train, how you told me about your husband and I told you about my father, how we hatched a plan to get rid of them both. Except after I did Eddie you got cold feet and tried to double-cross me.’

‘They won’t believe you. Why the hell should they?’

‘No, you’re the one they won’t believe. I mean, why would I do away with Eddie Wise? I didn’t even know the guy. And if you thought I’d murdered him, if you had even the slightest suspicion, then why didn’t you go straight to the cops? But you didn’t. Not even when I turned up on your doorstep. No, instead you brought me to a birthday party.’ Mona pulled a face. ‘It’s not going to look good, Sadie. It’s not going to look good at all.’

‘I’ll… I’ll just say that I thought you were crazy, that I thought you were making it up.’

‘And what about Joel?’

‘What about him?’

‘He’s going to wonder why you lied.’

‘I didn’t.’

‘You didn’t tell him the truth.’

‘He’ll understand.’

Mona wrinkled her nose. ‘Are you sure? Only he’s bound to question it all, isn’t he? Why you didn’t tell him straight out that we’d never met before or that I’m not really called Anne. Why would you keep that from him? And when he hears about the plans we made —’

‘We didn’t make any plans.’

‘It’s all going to look very odd. Yeah, he’s going to ask some awkward questions, like why you didn’t say anything when you came back to find me at your flat today or why you brought me here to his parents’ home when you thought I might be a cold-blooded killer.’

Sadie knew she was right. She could feel her chest growing tighter, the breath being squeezed out of her lungs. ‘I’ll explain,’ she said hurriedly. ‘I was confused, scared. I’ll tell him how I didn’t believe you’d actually done it.’

‘And you think he’ll be okay with that?’

‘He trusts me.’

‘For now.’ Mona leaned in close to Sadie, so close that their faces were almost touching. ‘But I don’t think the police will be as understanding. No, they’ll take a different view entirely. They’ll think you’ve been hiding something – and they’ll be right.’

‘Maybe I’ll take my chances.’

‘I don’t think so,’ Mona snapped. ‘You’re way too smart for that. You grass me up and we’ll both go to jail. I’ll swear to God that we were in this together. If I go down, Sadie, I’m taking you with me.’

Sadie stepped back, unable to bear the proximity of the girl. It was like standing too close to the Devil. ‘Why are you doing this to me? It’s not right. I never agreed to… You know I didn’t.’

Mona’s voice suddenly changed again, switching from a threatening tone to one that was almost wheedling. ‘Hey, it’ll be all right. You see if it isn’t. We’ll be okay. In a week or two everything will have settled down. The cops have got more important crimes to worry about than who killed a nobody like Eddie Wise.’

‘He wasn’t a nobody. He might not have been perfect but —’

‘By Christmas they won’t even remember his name.’

Sadie, battling against an ever growing panic, knew that any further remonstrations were pointless. You couldn’t argue with a crazy person and Mona was deranged. It was better, surely, not to antagonise her. What if she made a habit of carrying kitchen knives around? One wrong word and she might flip. No, it was better to try and keep the girl sweet until she could figure out a way of getting shut of her, of getting her away from the house. ‘Maybe,’ she said softly. ‘Maybe you’re right.’