I’ve read the note again and again, more times than Fatima has, more times than I can count, watching the way the words trail away into illegibility, following the progress of the drug in Ambrose’s straggling letters. I read it on the train up from Salten, and during the long wait at Hampton’s Lee. I read it while my own daughter lolled against my breast, her rosebud mouth open, her halting breath cobweb-soft against my skin, and I can only see it one way.

It is a father saving his child, and telling her to make his sacrifice worthwhile.

IT IS NEARLY ten when we get to the Mill, a journey full of delays, of waiting for trains, of watching Fatima break her fast on a station platform, when I know she would rather be with her family.

At Salten there’s more waiting while we call Rick and wait for him to complete another job, but at last we are ensconced in the back of his cab, Freya chewing her chubby knuckles in her car seat, Thea fidgeting beside me, biting at her bloodied nails, Fatima in the front, staring unseeingly into the night.

I know they are going through the same disbelieving round-and-round I have been running all day. If this is true, what did we do? And what does it mean for us all?

Losing our jobs … that would be bad enough. But accessory to murder? We could be looking at custodial sentences. Fatima and I could lose our kids. If this is true, will anyone in their right minds believe that we didn’t know what we were doing?

I try to imagine myself in a prison visiting room, Owen’s pinched face as he hands Freya over to a mother she barely recognises.

But my imagination fails – the only thing I know about prison is culled from Orange Is the New Black. I can’t accept that this is happening. Not to me. Not to us.

Rick goes as far as he can down the track before the wheels begin to spin, and then he lets us out and backs carefully up to the road, while we make our long, slow way down the track towards the Mill.

My heart is thumping. It looks as if the electricity is still out, but I can see a light flickering in Kate’s window. It’s not the steady stream of a bulb, though, but the soft uncertainty of a lamp, flickering a little as the curtains blow in the breeze.

As we get closer I realise I’m holding my breath, half expecting a repeat of the flooded bridge, but high tide won’t be for another few hours, and the walkway is still just clear of the rising waters. As we cross the rickety planks I see from Fatima and Thea’s faces what they are thinking – that if the waters rise, we may be stuck here for the night.

At last, though, we are assembled on the shrinking strip of muddy sand outside the door of the Mill.

‘Ready?’ Thea says, in a low voice and I shrug.

‘I’m not sure.’

‘Come on,’ Fatima says. She raises her fist, and for the first time I can remember, we knock on the Mill door, and wait for Kate to come and let us in.

‘You! What are you all doing here?’

Kate’s face, as she sees us all gathered on the doorstep, is surprised, but she stands back to let us in, and we file past into the darkness of the living room.

The only light is from the moonlight striking off the high waters outside the windows overlooking the Reach, and from the oil lamp in Kate’s hand, and as I pass her I get a flashback to her white face peering out from the shadows, watching me and Luc on the couch, and I cannot help but flinch.

‘The electricity’s still out,’ she says, her voice strange and detached. ‘Let me find some candles.’

I watch her as she hunts through the dresser, and my hand on the handle of Freya’s pram is trembling, I notice. Are we really going to do this? Accuse one of our oldest friends of killing her father?

‘Do you want to put Freya down in the back bedroom?’ Kate says over her shoulder, and I open my mouth to say no, but then nod. I don’t suppose we will be staying the night – not after we say what we’ve come to say – but there will be a scene either way, and I don’t want Freya mixed up in it.

I unclip the car-seat attachment from the pram, and then tell Fatima in a low voice, ‘I’ll be back in a sec. Wait for me.’

Freya slumbers on as I carry her carefully up the stairs to Luc’s room, and stays asleep as I deposit her gently on the floor and pull the door so it’s just ajar.

My heart is hammering as I walk back down to the ground floor.

The candles are lit, dotted around the place on saucers, and as I reach the sofa where Fatima and Thea are sitting, hands clasped anxiously around their knees, Kate straightens.

‘What’s all this in aid of?’ she asks mildly.

I open my mouth – but I don’t know what to say. My tongue is dry, sticking to the roof of my mouth, and my cheeks feel hot with shame, although I don’t know what, exactly, I’m ashamed of. My own cowardice, maybe?

‘Fuck, I’m getting a drink,’ Thea mutters. She picks up the bottle that’s on the sideboard and fills a whiskey tumbler. The liquid glints, black as oil in the candlelight as she knocks it back and wipes her mouth. ‘Isa? Kate?’

‘Yes please,’ I say, my voice shaking a little. Maybe it will help steady my nerves, help me to do this horrible, necessary thing.

Thea pours a glass, and as I swallow it back, feeling the roughness against my throat, I realise, I don’t know which is worse – the prospect that we’re wrong, and about to betray two decades of friendship on a misguided hunch. Or the idea that we’re right.

In the end it’s Fatima who stands up. She takes Kate’s hands, and I’m reminded once again of the steel beneath her compassion.

‘Kate,’ she says, and her voice is very low. ‘Honey, we came here tonight to ask you something. Maybe you’ve already guessed what it is?’

‘I don’t know.’ Kate’s face is suddenly wary. She pulls her hand away from Fatima and draws up a chair to sit opposite the sofa. I have a sudden image of her as a plaintiff and us as a panel of judges, grilling her, passing sentence. ‘Why don’t you tell me?’

‘Kate,’ I force myself to speak. It was me who brought my suspicions to the others – the least I can do is say them to her face. ‘Kate, I met Mary Wren on the way to the station earlier. She – she told me something that the police have discovered. Something I didn’t know.’ I swallow. Something is constricting my throat. ‘She – she said …’ I swallow again, and then force myself to say it in a rush, like ripping off a bandage, stuck to a wound. ‘She said that the police have discovered heroin in the wine bottle Ambrose was drinking from. She said that the overdose was oral. She said they’re not looking at suicide but – but –’

But I can’t finish.

It’s Thea who says it finally. She looks up at Kate from beneath the curtain of her long fringe, and the lamplight throws her face into shadows so that it looks so much like a skull, gleaming in the darkness, that I shudder.

‘Kate,’ she says bluntly, ‘did you kill your father?’

‘What makes you think that?’ Kate says, still in that oddly calm voice. Her face in the circle of lamplight is blank, almost sur-really so, compared to the naked pain on Fatima’s and Thea’s. ‘He overdosed.’

‘An oral overdose?’ I burst out. ‘Kate, you know that’s ridiculous. It’s a stupid way to commit suicide. Why would he do it when he had his works right there, ready to inject? And –’ and here my heart fails me, and I feel a stab of even greater guilt at what I’ve done, but I force myself on. ‘And there’s this.’

And I take the note out of my pocket, and throw it down on the table.

‘We read it, Kate. We read it seventeen years ago but I didn’t understand it until today. It’s not a suicide note, is it? It’s the note of a man who has been poisoned by his own child, and is trying to keep her out of prison. It’s a note telling you what to do – to go on, not to look back, to make his final action worthwhile. How could you, Kate? Is it true you were sleeping with Luc? Is that why you did it, because Ambrose was splitting you up?’

Kate sighs. She shuts her eyes, and puts her long slim hands to her face, pressing them against her forehead. And then she looks up at us all, and her face is very sad.