She takes a step closer. “So now you will tell me, once and for all, what happened that day. From the very beginning, right through to the argument and the moment you decided to kill my sister.”

She lowers her voice. “I told her everything that day, before the two of you went on your stupid walk. I thought it was about time she knew the truth. If you hadn’t killed her, she’d have told you, too. She’d have told you that she was your sister. How does that make you feel?”

Her words land like a blow, but I force myself to hold her gaze.

“I didn’t kill Alice. I never touched her. You have to believe me. We were arguing, yes, but I didn’t push her. I had a seizure. I blacked out.”

“Don’t lie!” she hisses through bared teeth. “You couldn’t stand it that Alice was so much prettier and more popular than you. You were eaten up with jealousy. Admit it.”

My eyes swim with unshed tears. I’m damned if I’ll cry in front of her. “You’re wrong! I loved Alice. She was my best friend.”

But even as I’m saying these words, I know that Catherine’s right. I was jealous of Alice. Of course I was. I hated the fact that she was everything I wasn’t: pretty, confident, popular. I hated the fact that she’d danced with Dave Farley even after he’d humiliated me in front of everyone. And I hated the way she kept doing that annoying little smile, the one she’d been doing ever since we set off on our walk, because I was so sure it was about him, and what had happened. I was so sure she was going to tell me he’d asked her out, and then it would all be over. I’d have lost her.

Catherine gives another of her scornful laughs. “Your best friend? You mean like your mum was my mum’s best friend?” She scowls. “Like mother, like daughter. Jealous, bitter bitches.”

“No! That’s not true! It was a silly row. We were thirteen, Catherine. Thirteen! We were children.” My words tumble out in juddery gasps. “I’d never have done anything to hurt her. It was an accident. A terrible accident!”

But how is she going to believe me when I don’t even believe myself? All those nightmares I’ve had over the years, horrible scenes of us fighting on the track, of me pushing and shoving her in fury. The shock and fear in her face. I’ve always told myself they were another symptom of post-traumatic stress, but what if those things actually happened?

I thought my discovery about Ross and Catherine was a dream, but it wasn’t, was it? That turned out to be real. So maybe the nightmares are real, too.

Maybe they’re memories.

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