Charlie and I are up on the battlements, looking out at the glitter of lights along the mainland. We left the others to their disgusting game. There’s something illicit about it, just the two of us up here. Something reckless. Perhaps it’s being on top of the world with the steep drop beneath us – invisible but very much there – adding a frisson of excitement, making everything feel slightly freighted with danger. Or that we’re cloaked by darkness. That anything could happen up here and no one would know.

‘It’s so good to have you here,’ I tell him. ‘You know you’re my best man, really?’

‘Thanks,’ he says. ‘It’s good to be here. Why did you choose this place?’

‘Oh, you know. My Irish roots. And it’s so exclusive, I like the idea of being first. There’s the remoteness, too: good for deterring any paps.’

‘They’d really try and get photos of his wedding?’ He sounds incredulous, like he doesn’t believe Will’s celebrity justifies it.

‘They might. And it’s so on-brand for Will, having his wedding in such a wild place.’

All of what I’ve told him is true, in a way. But not the whole truth.

I rest my head against his shoulder. I think I feel him go still. Perhaps it doesn’t feel quite so natural as it once did, being physically close like this. Come to think of it, did it ever?

Charlie clears his throat. ‘Can I ask you a question?’

He sounds serious. I sense a touch of wariness. ‘Go ahead.’ ‘He does makes you happy, doesn’t he?’

I lift my head a fraction off his shoulder. ‘What do you mean?’

I feel him shrug. ‘Just that. You know how much I care about you, Jules.’

‘Yes,’ I say. ‘He does. And I could ask you the same about Hannah.’ ‘That’s very different—’

‘Really? How so?’ I don’t want to hear his reply; I don’t need yet another person telling me that it has all been so quick, between Will and me. And then, because I’ve drunk more than I meant to this evening – and because when else am I going to be able to? – I say it: ‘Are you saying that you would have made me happier?’

‘Jules—’ He says it as a kind of groan. ‘Don’t do that.’ ‘Do what?’ I ask innocently.

‘We wouldn’t have worked. We’re friends, good friends. You know that.’ At that I feel him pulling away from me, retreating from the cliff edge.

Do I, though? And is he really so convinced of that? I know he wanted me once. I still think about that night. The memory I have returned to so many times … when I have needed some inspiration in the bath, for example. We have never spoken of it since. And because we haven’t, it has retained its power. I’m sure he still thinks about it too.

‘We were different people back then,’ he says, as though he might have read my mind. I wonder if he’s as convinced by his words as he’s making out. ‘I wasn’t asking because of anything like that,’ he says. ‘Not out of jealousy … or anything.’

‘Really? Because it sounds to me like you’re a bit jealous.’ ‘I’m not, I—’

‘Did I tell you how good he is in bed? That’s the sort of thing friends are meant to tell each other, isn’t it?’ I know I’m pushing it, but I can’t help myself.

‘Look,’ Charlie says. ‘I just want you to be happy.’

How bloody patronising. I lift my head fully away from his shoulder. I feel the distance between us expanding now, metaphorically as well as physically. ‘I’m perfectly capable of knowing what does and doesn’t make me happy,’ I say. ‘In case you haven’t noticed I’m thirty-four. Not a sixteen-year-old virgin totally in awe of you.’

Charlie grimaces. ‘God, I know. Sorry, I didn’t mean it like that. I care, that’s all.’

Something has suddenly occurred to me. ‘Charlie?’ I ask. ‘Did you write me a note?’

‘A note?’

I hear the answer to my question in his confusion. It wasn’t him. ‘It’s nothing,’ I say. ‘Forget it. You know what? I think I’m going to

turn in. If I go now, I can get eight hours’ sleep before tomorrow.’ ‘OK,’ he says. I sense that he is relieved I’ve called it a night and that

pisses me off.

‘Give me a hug?’ I ask. ‘Sure.’

I lean into him. His body is softer than Will’s, so much less taut than it used to be. But the scent of him is the same. So familiar, somehow, which is strange – considering how long it’s been.

It’s still there, I think. He must feel it too. But then attraction never really goes away, does it? I’m sure of it: he’s jealous.

When I get back to the room Will’s getting undressed. He grins at me, I move toward him.

‘Shall we pick up where we left off earlier?’ he murmurs.

It’s one way, I think, to erase the humiliation of that conversation with Charlie.

I tear open the remaining buttons on his shirt, he rips one of the straps of my jumpsuit trying to get it off me. It’s always like the first time with him – that haste – only better, now we know exactly what the other wants. We fuck braced against the bed, him entering me from behind. I come, hard. I’m not quiet about it. In a strange way, it feels as though much of the evening since we got interrupted earlier has been a kind of foreplay. Feeling the gaze of the others upon us: envious, awed. Seeing in their reactions to us how good we look together. And yes, the hurt of having crossed a line with Charlie and being rebuffed. Maybe he’ll hear us.

Afterwards Will goes for a shower. He takes impeccable care of himself – his routine even makes my own look rather slapdash. I remember being a little surprised when I realised his permanently brown face wasn’t actually due to the constant exposure to the elements but to Sisley’s self-tan, the same one I use.

It’s only now, sitting in the armchair in my robe, that I become aware of a strange odour, more powerful than the evanescently marine scent of sex. It is stronger, undeniably the smell of the sea: a briny, fishy, ammoniac tang at the back of the throat. And as I sit here it seems to gather itself from the shadowy corners of the room, gaining texture and depth.

I go to the window and open it. The air outside is pretty icy, now that it’s dark. I can hear the slam of the waves against the rocks down below. Further out the water is silver in the light of the moon, like molten metal, so bright that I can hardly look at it. You can see the swell in it even from here, great muscular movements beneath the surface, full of intent.

I can hear a cackling above me, up on the roof, perhaps. It sounds like a gleeful mocking.

Surely, I think, the smell of the sea should be stronger outside than in? Yet the breeze that wafts in is fresh and odourless by comparison. I can’t make sense of it. I reach over to the dressing table and light my scented candle. Then I sit in the chair and try for calm. But I can practically hear the beat of my own heart. Too fast, a flutter in my chest. Is it just the aftermath of our exertions? Or something more than that?

I should talk to Will about the note. Now is the moment, if I’m ever going to do it. But I’ve already had one confrontation this evening – with Charlie – and I can’t quite bring myself to face the thing head-on, to plough ahead and raise it. And it’s probably nothing. I’m 99 per cent sure, anyway. Maybe 98.

The door to the bathroom opens. Will steps into the room, towel knotted around his waist. Even though I have just had him I’m momentarily distracted by the sight of his body: the planes and ridges of it, the muscles corded in stomach, arms and legs.

‘What are you doing still up?’ he asks. ‘We should get some rest. Big day tomorrow.’

I turn my back to him and drop my robe to the floor, sure I can feel his eyes on me. Enjoying the power of it. Then I lift the cover and slip into the bed and as I do my bare legs make contact with something. Solid and cold, the consistency of dead flesh. It seems to yield as I push my feet unwittingly into it and yet at the same time to wrap itself around my legs.

‘Jesus Christ! Jesus Fucking Christ!’

I leap from the bed, trip, half sprawl on the floor. Will stares at me. ‘Jules? What is it?’

I can hardly answer him at first, too scared and repulsed by what I just felt. The panic has risen into my throat in a choke. The shock reverberates through me, deep and visceral and animal. It was the stuff of a nightmare – the sort of thing you dream about finding in your bed, only to wake in a chill sweat and realise it was all in your imagination. But this was real. I can still feel the cold imprint of it against my legs.

‘Will,’ I say, finally finding my voice. ‘There’s something – in the bed. Under the covers.’

He strides over in two great bounds, takes the duvet in both hands and rips it away. I can’t help screaming. There, in the middle of the mattress, sprawls the huge black body of some marine creature, tentacles stretching in all directions.

Will leaps back. ‘What the fuck?’ He sounds more angry than frightened. He says it again, as though the thing on the bed might somehow answer for itself: ‘What the fuck …?’

The smell of the sea, of briny, rotting things, is overpowering now, emanating from that black mass on the bed.

And then quickly, recovering much more rapidly than I do, Will moves closer to it again. As he puts out a hand I shout, ‘Don’t touch it!’ But he has already grasped the tentacles, given them a yank. They come free, the thing seems to break apart – horribly, sickeningly. It was there while we fucked, waiting for us beneath the covers …

Will gives a short, hard laugh, entirely without humour. ‘Look – it’s only seaweed. It’s bloody seaweed!’

He holds it aloft. I lean closer. He’s right. It’s the stuff I’ve seen strewn along the beaches here, great thick, dark ropes of it washed up by the waves. Will tosses it on to the floor.

Gradually, the whole scene loses its grotesque edge and devolves into a chaotic mess. I become acutely aware of the indignity of my position, sprawled naked on the floor. My heartbeat slows, and I find it easier to breathe.

But then … how did this even end up here? Why is it here?

Someone has done this to us. Someone brought it in and hidden it beneath the duvet, knowing we’d only discover it when we climbed into bed.

I turn to Will. “Who could have done this?” He shrugs. “Well, I have my suspicions.” “What do you mean?”

“It was a prank we used to pull on the younger boys at school. We’d hike down the cliff path and collect as much seaweed as we could carry, then hide it in their beds. So I’d guess it was Johnno or Duncan—maybe all the guys. They probably thought it was hilarious.”

“You call this a prank? We’re not in school, Will; it’s the night before our wedding! What the hell?” In a way, my anger feels like a release.

Will shrugs. “It’s not a prank for you; it’s for me. You know, for old times’ sake. They didn’t mean for you to get upset—”

“I’m going to wake them up and find out who did this. I’ll show them just how funny I think it is.”

“Jules.” Will grabs my shoulders, then speaks softly, “If you do that … you might say things you’ll regret. It could spoil tomorrow, don’t you think? It could change the whole vibe.”

I can see his point, sort of. God, he’s always so reasonable—sometimes it’s infuriating, always taking the calm approach. I look at the black mass on the floor; it’s hard to shake the feeling that there’s a darker message behind it.

“Look,” Will says gently. “We’re both tired. It’s been a long day. Let’s not stress about it now. We can grab a new sheet from the spare room.”

The spare room was meant for Will’s parents. They were put off by the idea of actually staying on the island. Will didn’t seem surprised. “My father’s never been impressed by anything I’ve done—getting married is no exception.” There’s a bitterness in his voice. He rarely talks about his father, which somehow makes me feel that his influence looms larger over Will than he’s willing to admit.

‘Get a new duvet, too,’ I tell Will now. I’m half tempted to say I want to swap to the other room. But that would be irrational, and I pride myself on being the opposite.

‘Sure.’ Will gestures to the seaweed. ‘And I’ll sort out this, too – I’ve dealt with much worse, trust me.’

On the programme Will has escaped from wolves and been swarmed by vampire bats – though he’s never far from the help of the crew – so this must all seem a little pathetic to him. A bit of seaweed on the sheets is hardly a big deal, in the grand scheme of things.

‘I’ll have a word with the guys tomorrow morning,’ he says. ‘Tell them they’re fucking idiots.’

‘OK,’ I say. He’s so good at providing comfort. He’s so – well, there’s only really one word for it – perfect.

And yet, in this moment, with particularly nasty timing, the words on that horrible little note surface.

Not the man he says he is … cheat … liar … Don’t marry him.

‘A good night’s sleep,’ Will says, soothingly. ‘That’s what we need.’

I nod.

But I don’t think I’m going to sleep a wink.