The black sky envelopes us as we get nearer the cliff’s edge, and I’m panicking that the flashlights we’re each carrying aren’t up to the job of keeping me from falling off the side to my death. As panic sets in, vertigo is triggered, and I’m taking tiny steps along the gravel path down the cliff, almost shuffling.

“We must have a death wish or something,” I mutter.

“Do you want me to hold your elbow?” Ondine asks and, although I really would like her to hold my elbow, I’d also like to hang onto any shred of dignity I might have left.

“I’m okay – must be night blindness.”

“Sure,” she says, unconvinced.

After what seems like several hours but is more likely minutes, I finally set foot on the rocky beach. My legs are like jelly, but I’m so relieved to be on firm ground again that I give a little whoop. Ondine shines her flashlight in the direction of the islands she pointed out earlier and asks me what I can see.

“You mean the islands? I can just about make out their contours in this light.”

“Tell me exactly what you see. Be specific.”

I stare at the shapes, certain that I’m being tested but not sure about what. “I see a tall black mound that slopes down to a flatter surface at its eastern edge. A bit behind the larger island is another shape, more like a single mound, rising up to the central curved peak and back down the other side, almost like a mirror image of itself.”

Ondine turns the flashlight off, and tells me to keep staring at the space. “What do you see now?”

“I can still see the islands, but it’s so dark that doesn’t seem possible. It must be an imprint on my eyelids, or my brain holding onto the image it just saw.”

“Okay, now what if I tell you that all most people ever see, in daylight or at night, is the large island?” She pauses for a moment, then adds, “Most people never, ever see the small island.”

“What are you talking about?”

“It’s an invisible island. Or, to be more accurate, it is invisible to all but those with the sight.”

“The sight?”

“Those of us who have some kind of connection to other planes of being.”

I stand still and quiet, staring out at the two shapes in the sea. “Are you going to tell me what your connection is?”

“I am, in the fullness of time. For now, let’s just say I didn’t have any plans to come back here to Ballaig, not ever, if I’m honest. The whole time I’ve thought that if you’re given this connection, but you never really wanted it, then maybe if you ignore it, it will just go away. But deep down I think I knew that wasn’t ever going to happen.”

I hear her take a sharp breath, and then she continues. “When I first became aware of this connection, it confirmed everything my parents told me when I was growing up – that there is something wrong with me, that I’m not normal. I just didn’t expect to be this abnormal, and in this way. I think I thought if I rejected this, I could prove them wrong.”

Her fingers are warm as she laces them in mine. “Come here, I’ve got something to show you.” She starts walking away from the shoreline, back towards the cliff, and my body must tense up because she says, “It’s okay – we’re not climbing anything.”

She takes small steps, the pebbles crunching under her feet, and I shuffle along behind her, trying not to step on her feet, which I can’t see. The salty tang in the air shifts, and I smell something damp and mossy, almost as though we’re inside a cave. I can still see the edges of the islands on the horizon, but the smell combined with the damp chill has me convinced that we have entered a cave, or a tunnel. Claustrophobic panic spikes through me, the kind I always get when I’m in a confined space. But it’s ridiculous to feel this way when I can see the evidence that we’re still outside.

I’m about to ask Ondine what’s happening when I hear it – the loud, pounding rush of water. I gasp, and stop short, and Ondine squeezes my hand. “It’s okay – you’ll see it in a second.”

We take a few more steps forward and then somehow – impossibly – we are standing inside a tall cave, bright with natural light streaming in through one side, where the waterfall tumbles over the edge. The stone inside the cave is ochre-coloured, and I reach out to touch one of the walls, wanting to see if it’s firm to my touch, or just an illusion. The stone is rough, cool, and damp.

My senses of vision and touch are telling me that we are standing inside a cave in daylight, even though I know we’re on a pebbly beach in Scotland, in the middle of the night. “How is this possible?” I ask Ondine, my voice echoing loudly in the space.

“How can we see the second island, when almost no one else can?”

“You mean this cave is invisible, too?”

“Not to everyone.”

“And how can we carry on a conversation over the sound of the waterfall?” The flashlight illuminates her face, and she’s giving me a happy, I-can’t-believe-it-either look. “Ondine, what’s going on?”

“I don’t have the answers. It’s not something we can understand with facts or logic. All I know is that I discovered this one night when I came down here to get away from my thoughts. But the thoughts were about how I must be going crazy, and then I found myself in a bright cave at midnight. I tried taking photos to show Elena, but they just turned out black.”

She pauses, looking around as though she still can’t believe what she’s seeing. “I told her anyway, and she believed me.”

“She did?”

Ondine looks me in the eye and nods. “She did – because she’s seen it, too.”

“Elena has the sight.”

“She does. And she told me there’s someone else who’s been here, but she won’t tell me who it is.”

The mist from the waterfall is cool on my face, and I puff my cheeks out, shaking my head. “But what does this mean? Why can we see it?”

“Do you mean that in an existential way?”

“No, I mean, why are we able to be here right now? Is it a portal to another time and place?”

Ondine shakes her head. “I’ve been here maybe five times in total. I discovered it by accident, and I returned because it’s a place to come when I need some time alone – to just be. It’s always the same. If it was a portal, wouldn’t something have happened to me already?”

Before I can answer, I’m distracted by shadows moving across the wall on the other side of Ondine. I spin around and look behind me – all around me – but see nothing.

“What? What is it?”

“Shadows. I definitely saw shadows on this wall.”

“How is that possible, if we’re the only ones here?”

As Ondine is speaking, I see them flicker across the wall again. “There! It happened on that wall again. Just watch, and wait.”

But the next time it happens, I see the shadows but Ondine doesn’t. I make her watch and wait, despite her increasing frustration, until I’ve seen the shadows a total of six times, yet she never once sees them.

“Why can only you see them?” she asks, upset.

“Maybe it’s a portal for me only?”

“Why would I be able to see it too, then?”

“I don’t know – maybe there’s another portal for you?”

“But I can still hang in your portal. Does that make any sense?”

My eyes widen involuntarily at the question. “Does any of what’s happening to us make any sense?”

She laughs. “Fair point.”

I need to ask her a question, one which I hope she won’t refuse to answer. “Ondine, I know you aren’t ready to talk about it, but can I just ask if your – connection – has anything to do with water?”

She bites her lip. “No – not in the way yours does.” And then her eyes widen, and she says, “But the island does. Nester Island is definitely significant, but maybe Hallowtide is, too.”

“So if we could get to Hallowtide, we could find out if I can hang in your portal.”

Ondine laughs and says, “Is it possible to sail to an invisible island?”

“Is it possible to stand inside an invisible cave?”

“This is too weird.”

“Agreed.”

“I think we need to talk to Elena.”

“Also agreed.” I try to make my voice as gentle as possible when I say, “Ondine? Do you think it might be time to tell me about it?”

She turns to look me straight in the eye and says, giving me a look that’s fierce and vulnerable at the same time. “I don’t think I can avoid it much longer. But first, let’s find Elena.”