‘Lord help us,’ breathed Dad, and I could see connections sparking in his brain. He gritted his teeth. ‘It was you who sent the tarred feather to the Courtaulds.’

He spoke half in anger, half in sheer wonder.

‘Yes,’ said Mum. Her face was white, her eyes were like dark holes. ‘I spilled hot tar on myself and couldn’t clean it properly, so it got infected.’

Dad looked at her with fury and disgust and took a step towards her.

‘You wrote the letters.’

‘Yes,’ she said again, and she made a motion with her hands, either to shove him away from her or to draw him closer.

‘Why?’

‘I’ve nothing against Stephen, but Ginie – that’s a different story. I wanted to hurt her. She was taking you away from me.’

For a moment, I thought Dad was going to hit her.

‘I couldn’t stop thinking about the two of you,’ Mum went on. ‘It kept going round in my head.’ She gave a low moan and shut her eyes, pressing her knuckles into them as though she could crush out the bad thoughts. Dad gave her a deadly look.

‘Sending the letters made me feel better,’ she said, opening her eyes wide, ‘but you see, the good feelings never lasted.’ She sighed, shaking her head regretfully. ‘So I had to write again and again. I was addicted.’

Dad’s face was twitching. ‘Are you quite mad?’

Mum’s blue eyes had a new light in them and an ugly flush bloomed on her thin cheeks. ‘I’m mad for you, Mark,’ she said, in a high-pitched tone I’d never heard before. She tossed her hair in a gruesome show of flirtatiousness.

‘Dear Christ in hell,’ muttered Dad.

‘You haven’t touched me in so long. . . so long!’ she wailed.

Everyone was silent. When Mum began to speak again, it was in a soft, resigned voice that made me hope she wasn’t crazy after all.

‘I felt you slipping away from me and it just about destroyed me. Oh, the pain was awful – I couldn’t eat, couldn’t sleep. Just raw waves of pain. In here.’ She pushed a hand against her chest.

Dad shook his head slowly.

‘I shouldn’t have written those letters. I don’t know why I did. But everything changed.’ She swallowed. Her face was wretched. ‘I don’t know what’s happening anymore. Why have things turned out like this? I didn’t want them to turn out like this. But when I saw how you looked at her. . . It’s Ginie’s fault,’ she snarled. ‘She deserves to be punished for what she has done to us.’

Dad stared and stared at Mum without speaking, until she began to shuffle her feet and her eyes grew shifty, but there was a glint of sly satisfaction in them that made my blood run cold.