We talk until night fades into morning.

The spectrum of colour moves from the lushness of navy into streaks of the palest pearl. When the sun finally rises, the flames of dawn play across our faces as we lie on our stomachs on the rug in the sitting room, not having been to bed.

My notepad is filled with dozens of shorthand pages of testimony, and I’ve had to use my dictaphone’s spare memory card. For once, I remember Colin’s instructions, and I film Sara – I can’t bring myself to call her Catherine – on my mobile phone. My hand shakes and the footage is grainy, the sound quality poor, and I’ll know he’ll complain, but she does not want a videographer or a photographer here, or any money for this interview.

All she wants is to tell the truth.

It’s explosive.

There’s a convincing clarity to her story, an honesty about the way she stumbles through this tale of broken families and murder and sibling love. She refuses to condemn her sister. Or the police. Or the legal system. Or me.

She just wants to be free again.

Part of me wants to applaud her courage. But the other part – the self-interested part – knows that she will make headlines around the world with this extraordinary story of personal sacrifice. That now, even more than before, she will not be able to escape the truth of who she is and the lies she told. That although I lied too, she is the one who will be hounded and questioned, and face potential charges of perjury, of wasting police time. Her choices will be examined and discussed, turned over and criticized. She will be mocked, deified, ridiculed and lauded.

But then I think, She knows this, the risk of it, and her need to confess – to cleanse herself for the love of her daughter – outweighs even that.

I dare not think what Lawrie will say when he realizes I’ve cut him out of the story of a lifetime and come here alone, or what the commentators and the police will make of my part in it all. But it will be worth it – whatever the cost – to be free of the guilt I have borne for so long.

Sara gives a crooked grin for the camera, as if asking not to be judged too harshly. ‘So that’s my story. I’ve carried it for years, and whatever happens now, I’m lighter for it.’ And her smile is one of such heartbreaking relief that tears prick my eyes.

We look at each other – properly look – and then, impossibly, we laugh.

The hug she gives me feels like coming home.

The day is awake now, the birds in full song, the fields still covered in their coat of frost. We drink tea and eat boiled eggs and toast with marmalade, and she yawns.

‘Go to bed,’ I say. ‘Get some sleep.’