'Er, Jack … excuse me a minute.' I shoot him a bright smile. 'I just need to … take this call.'

With trembling legs I hurry to the corner of the courtyard, well away from earshot.

'Jemima, you promised you wouldn't do anything!' I hiss. 'You swore on your Miu Miu ponyskin bag, remember?'

'I haven't got a Miu Miu ponyskin bag!' she crows triumphantly. 'I've got a Fendi ponyskin bag!'

She's mad. She's completely mad.

'Jemima, what have you done?' I manage. 'Tell me what you've done.'

My heart is thudding in apprehension. Please don't say she's scraped his car. Please.

'An eye for an eye, Emma! That man totally betrayed you, and we're going to do the same to him. Now, I'm sitting here with a very nice chap called Mick. He's a journalist, he writes for the Daily World …'

My blood runs cold.

'A tabloid journalist?' I manage at last. 'Jemima, are you insane?'

'Don't be so narrow-minded and suburban,' retorts Jemima reprovingly. 'Emma, tabloid journalists are our friends. They're just like private detectives … but for free! Mick's done loads of work for Mummy before. He's marvellous at tracking things down. And he's very interested in finding out Jack Harper's little secret. I've told him all we know, but he'd like to have a word with you.'

I feel quite faint. This cannot be happening.

'Jemima, listen to me,' I say in quick, low tones, as though trying to persuade a lunatic down off the roof. 'I don't want to find out Jack's secret, OK? I just want to forget it. You have to stop this guy.'

'I won't!' she says like a petulant six-year-old. 'Emma, don't be so pathetic! You can't just let men walk all over you and do nothing in return. You have to show them. Mummy always says—' There's the sudden screeching of tyres. 'Oops! Tiny prang. I'll call you back.'

The phone goes dead.

I am numb with horror.

Frantically I jab her number into my phone, but it clicks straight on to messages.

'Jemima,' I say as soon as it beeps. 'Jemima, you have to stop this! You have to—' I stop abruptly as Jack appears in front of me, with a warm smile.

'It's about to start,' he says, and gives me a curious look. 'Everything all right?'

'Fine,' I say in a strangled voice, and put my phone away. 'Everything's … fine.'

TWENTY-FIVE

As I walk into the auditorium I'm almost lightheaded with panic.

What have I done? What have I done?

I have given away Jack's most precious secret in the world to a morally warped, revenge-wreaking, Prada-wearing nutcase.

OK. Just calm down, I tell myself for the zillionth time. She doesn't actually know anything. This journalist probably won't find out anything. I mean, what facts does he actually have?

But what if he does find out? What if he somehow stumbles on the truth? And Jack discovers it was me who pointed them in the right direction?

I feel ill at the thought. My stomach is curdling. Why did I ever mention Scotland to Jemima? Why?

New resolution: I am never giving away a secret again. Never, ever, ever. Even if it doesn't seem important. Even if I am feeling angry.

In fact … I am never talking again, full stop. All talking ever seems to do is get me into trouble. If I hadn't opened my mouth on that stupid plane in the first place, I wouldn't be in this mess now.

I will become a mute. A silent enigma. When people ask me questions I will simply nod, or scribble cryptic notes on pieces of paper. People will take them away and puzzle over them, searching them for hidden meanings—

'Is this Lissy?' says Jack, pointing to a name in the programme, and I jump in fright. I follow his gaze, then give a silent nod, my mouth clamped shut.

'Do you know anyone else in the show?' he asks.

I give a mute 'who knows?' shrug.

'So … how long has Lissy been practising?'

I hesitate, then hold up three fingers.

'Three?' Jack peers at me uncertainly. 'Three what?'

I make a little gesture with my hands which is supposed to indicate 'months'. Then I make it again. Jack looks totally baffled.

'Emma, is something wrong?'

I feel in my pocket for a pen — but I haven't got one.

OK, forget not talking.

'About three months,' I say out loud.

'Right.' Jack nods, and turns back to the programme. His face is calm and unsuspecting, and I can feel guilty nerves rising through me again.

Maybe I should just tell him.

No. I can't. I can't. How would I put it? 'By the way, Jack. You know that really important secret you asked me to keep? Well, guess what …'

Containment is what I need. Like in those military films where they bump off the person who knows too much. But how do I contain Jemima? I've launched some crazed human Exocet missile, fizzing around London, bent on causing as much devastation as she can, and now I want to call her back, but the button doesn't work any more.