I stand, picking up Freya who gives a hiccup of surprise and drops the book.

‘I might go for a walk,’ I say aloud. Fatima barely looks up from the screen.

‘Good plan. Where will you go?’

‘I don’t know. Salten village, probably.’

‘You sure? It’s a good three or four miles.’

I suppress a spurt of irritation. I know the distance as well as she does. I walked it often enough.

‘Yes, I’m sure,’ I say evenly. ‘I’ll be fine – I’ve got good shoes, and Freya’s buggy’s quite sturdy. We can always get a taxi back if we’re tired.’

‘OK, well, have fun.’

‘Thanks, Mum,’ I say, letting my annoyance break through, and she looks up and grins.

‘Oops, was I doing that thing? Sorry, I promise I won’t tell you to wear a coat and make sure you’ve done a wee.’

I crack a smile as I strap Freya into her buggy. Fatima could always make me laugh, and it’s hard to be pissed off while you’re grinning.

‘The wee might not be bad advice,’ I say, pulling on my walking sandals. ‘Pelvic floor ain’t what it used to be.’

‘Tell me about it,’ Fatima says absently, tapping out a reply. ‘Remember those Kegels. And squeeze!’

I laugh again, and glance out of the window. The sun is beating down on the glassy, glinting waters of the Reach, and the dunes shimmer with heat. I must remember Freya’s sunscreen. Where did I pack it?

‘I saw it in your washbag,’ Fatima says, speaking around the pencil gripped between her teeth. My head jerks up.

‘What did you say?’

‘Sunscreen, you just muttered it as you were looking through Freya’s nappy bag. But I saw it upstairs in the bathroom.’

God, did I really say it aloud? I must be going mad. Perhaps I’ve got so used to being alone with Freya on maternity leave, I’ve started talking to myself, voicing my thoughts aloud to her at home in the silent flat?

The thought is a creepy one. What else might I have said?

‘Thanks,’ I say briefly to Fatima. ‘Keep an eye on Freya for a sec?’

She nods, and I run upstairs to the bathroom, my walking shoes clomping on the wooden stairs.

When I try the door, it’s locked, and I can hear sloshing from within, and belatedly I remember that Kate is in there.

‘Who is it?’ Her voice is muffled by the door, and echoey.

‘Sorry,’ I call back. ‘I forgot you were in here. I’ve left Freya’s suncream inside – can you pass it out?’

‘Hang on.’ I hear a rush of water, and then the lock clicks, and a slosh as Kate gets back into the tub. ‘Come in.’

I open the door cautiously, but she’s fully submerged beneath icebergs of foam, her hair drawn up into a straggly topknot showing her long slim neck.

‘Sorry,’ I say again. ‘I’ll be quick.’

‘No worries.’ Kate sticks a leg out of the tub and begins to shave it. ‘I don’t know why I locked it anyway. It’s not like it’s anything you lot haven’t seen before. Are you going out?’

‘Yes, I’m going for a walk. Maybe to Salten, I’m not sure.’

‘Oh, listen, if I give you my card, could you get out two hundred pounds so I can pay you and Fatima back?’

I have found the suncream now, and I stand, twisting the cap in my hands.

‘Kate, I – look, Fatima and I … we don’t …’

God, this is hard – how to say it? Kate has always been proud. I don’t want to offend her. How can I say what I’m really thinking, which is that Kate, with her crumbling house and broken-down car, clearly can’t afford two hundred pounds, whereas Fatima and I can?

As I’m scrabbling for the right words, an image flashes sharply into my mind, distracting as a jab from a stray pin when you’re dredging for your purse in your handbag.

It’s the note, slick with blood. Why don’t you throw this one in the Reach too?

I feel suddenly sick.

‘Kate,’ I blurt out, ‘what really happened out there? With Shadow?’

Her face goes suddenly blank, unreadable. It’s like someone has drawn a shutter down.

‘I should have shut the gate,’ she says flatly, ‘that’s all.’ And I know, I know she is lying. Kate has become as remote as a statue – and I know.

We swore never to lie to each other.

I stare at her, half submerged in the cloudy, soapy water, at the uncompromising set of her mouth; thin, sensitive lips, clamped together, holding back the truth. I think about the note that I destroyed. Kate and I both know she is lying, and I am very close to calling her on it – but I don’t quite dare. If she’s lying, it must be for a reason, and I’m afraid to find out what that reason might be.

‘All right,’ I say at last. I’m conscious of my own cowardice as I turn to go.

‘My card’s in my wallet,’ Kate calls as I shut the door behind me. ‘The PIN’s 8431.’

But, as I clatter down the stairs towards Fatima and the still-sleeping Freya, I don’t even try to remember it. I’ve got no intention of taking her card, or her money.

OUTSIDE, PUSHING FREYA’S buggy along the sandy track that leads up the side of the Reach, away from the Mill, I begin to feel the oppressive mood lift.

The day is calm and quiet, and the gulls are bobbing tranquilly on the rising tide, the waders stalking the mudflats with intent concentration, darting their heads down to pluck up unsuspecting worms and beetles.

The sun is hot on the back of my neck, and I adjust the sunshade on Freya’s pram, and wipe the residue of the sunscreen I have slathered over her fat little limbs onto the back of my neck.

The smell of blood is still in my nostrils, and I long for a breath of air to blow it away. Was it Shadow? I can’t tell. I try to think back to the spilled guts and the whining dog; were those tears from a strong jaw, or cuts from a knife? I just don’t know.

There is one thing for sure, though – Shadow could not have written that note. So who did? I shiver in the bright sunshine, the malevolence of it suddenly striking through to my bones. All at once, I have a strong urge to snatch up my sleeping baby and press her into my breast, hugging her to me as if I can fold her back inside myself, as if I can protect her from this web of secrets and lies that is closing in around me, dragging me back to a long-ago mistake that I thought we’d escaped. I am starting to realise that we didn’t, none of us. We have spent seventeen years running and hiding, in our different ways, but it hasn’t worked, I know that now. Perhaps I always knew that.

At the end of the lane, the track opens up to a road that leads in one direction to the station, and in the other across the bridge into Salten itself. I pause on the bridge, rocking Freya gently to and fro, surveying the familiar landscape. The countryside around here is fairly flat, and you can see a long way from the shallow vantage point of the bridge. In front of me, black against the bright waters of the Reach, is the Mill, looking small in the distance. To the left, on the other side of the river, I can just see the houses and narrow twittens of Salten village.

And to the right, far off in the distance, is a white shape that glimmers over the tips of the trees, almost invisible against the sun-bleached horizon. Salten House. Standing here, it’s impossible to pick out the route we used to walk across the marsh, when we broke out of bounds. Perhaps it’s overgrown, but now I marvel at our stupidity, remembering the first time, that chilly October night, dusk already drawn in as we climbed out of the window onto the fire escape, torches between our teeth, boots in our hands so we didn’t wake the teachers as we crept down the rattling iron structure.

At the bottom, we shoved our feet into wellingtons (‘Not shoes,’ I remember Kate telling us, ‘even after the summer we’ve just had, it’ll be muddy’) and then we set off, running lightly across the hockey fields, suppressing our laughter until we were far enough away from the buildings that no one would hear us.

That first part was always the dangerous bit, particularly as the days grew longer, and it was light outside long after curfew. From Easter onwards, any teacher looking out of their window would have seen the four of us fleeing across the close-cropped grass, Thea’s long legs eating up the distance, Kate in the middle, Fatima and me puffing behind.