The body of Oliver Hartley lay in the kitchen of the Bell Rock Light, and also it did not. The undertaker had rowed out four days ago with a pine box and a length of sailcloth, and also no one had come. William had buried his father in the churchyard at Marazion, in the plot beside his mother, with the vicar reading from the Book of Common Prayer, and also Oliver Hartley was still sitting in his chair by the stove, his sweater folded across his lap, his tea gone cold beside the logbook, his eyes open and looking at William with an expression that was not accusation but patience, the patience of a man who had waited twelve years and could wait twelve more.

William accepted both realities. He did not choose between them. He did not need to. The world, he had learned in the eleven days since the fever, was not a single thing but a superposition of possibilities, each one true in its own frame, each one demanding its own response. He served tea to his father's body. He wound the clockwork mechanism that turned the lens. He read the logbook entries about the Navy expedition and the trench and the creatures that pulsed at four point seven hertz. And he spoke to his father, who was dead and alive, who was buried in the churchyard and sitting in the kitchen, who had died of fever and also had not.

The lamp burned through the night and also burned during the day. The fog pressed against the glass and also lifted. The great Fresnel lens turned and also stood still, and William observed these things without needing to resolve them, without needing to pick one state and discard the other. The world presented itself in doubles, in overlapping images, in truths that contradicted each other and yet coexisted in the same moment, the same room, the same boy's mind. This was not madness. This was simply the way things were. Madness was the insistence that only one truth could occupy a given space. Sanity was the acceptance that every space contained multitudes.

Was I a good son, William asked the empty chair and the occupied chair. Did I do what you wanted.

The chair did not answer and the chair answered. The answer was yes and no. William had been a good son, but being a good son was not the same as being ready. He was fourteen years old. He was not ready for the creatures in the trench, for the Navy conspiracy, for the barometer that had shattered at sixty fathoms and the water that was denser than water should be. He was not ready for any of it, and he was exactly as ready as he needed to be. Both statements were true. They occupied the same space without contradiction.

Old Tom Hedges came to the lighthouse on the twelfth day. He brought bread and salted fish and a jar of tea. He found William in the lantern room, sitting on the gallery with the logbook in his lap, his feet dangling over the edge. The fog was thick enough to cut, and the lens turned behind them like a mechanical heartbeat, and Tom looked at William and saw a boy of fourteen and also a man of forty, a child who had lost his father and a keeper who had inherited a weight that no one should have to carry.

They say your father was mad, Tom said. They say the fever took his mind before it took his body. They say there is nothing in the trench, no creatures, no pulse, no Navy cover-up. They say it was all a delusion, a hallucination brought on by isolation and grief and the constant sound of the sea.

William nodded. They are right, he said. My father was mad. The fever took his mind. The creatures are a delusion.

And also, he thought, my father was the sanest man in Cornwall. The fever was real but the creatures were also real. The Navy did cover up the expedition. The truth is buried. Both things are true. The contradiction does not collapse. It exists, and I exist within it, and I will not choose sides because choosing sides would be a lie.

Tom looked at him strangely. The boy's voice had sounded different, somehow. Older. Calmer. As if he were speaking from some other place, some other frame of reference where certainty was not required and truth was not singular.

You are not making sense, Tom said. Either your father was mad or he was not. Either the creatures are real or they are not. You cannot have it both ways.

I do not have it both ways, William said. Both ways have me. I am held in a state of possibility, and I will not be the one to collapse it. The wave function of my father's life and death is unresolved. The creatures pulse and do not pulse. The Navy conspired and did not conspire. Oliver Hartley was a madman and a prophet and a lighthouse keeper and a scientist and a father and a ghost. He was all of these things and none of them, and any attempt to reduce him to a single truth would be an act of violence against what he actually was.

Tom set down the bread and the fish. He looked at the logbook in William's lap. He looked at the empty chair in the kitchen below. He looked at the water around the rock, which was grey and flat and also full of something moving, something deep, something that might have been creatures or might have been currents or might have been nothing at all.

I do not understand you, Tom said.

William smiled. That is all right, he said. I do not understand myself. Understanding is not required. The only requirement is that I keep the light burning. That was my father's last instruction to me, in the fever and also in the logbook and also in the silence between his words. Keep the light burning. The rest is superposition.

The naval cutter arrived on the fifteenth day. The officers who came ashore were two men in grey coats, and they were looking for evidence of a Navy expedition that had happened twelve years ago and also had not happened. They were following orders that were legitimate and illegitimate, issued by an Admiralty that was both protecting national security and covering up a crime. They searched the lighthouse and they found nothing, and also they found everything. They found the logbook, which contained the truth about the trench and the creatures and the pulse, and also the logbook was just a logbook, a record of weather and shipping and oil consumption, nothing more.

We have received reports, the senior officer said. Reports that Oliver Hartley was spreading dangerous rumours. Reports that he claimed to have discovered something in the trench. Reports that he was a threat to national security and also a harmless old man who had spent too many years alone on a rock.

My father is dead, William said. He died of fever eleven days ago. He is buried in the churchyard at Marazion.

The officer looked at William. The boy's face was calm, serene almost, as if he were looking at something far away, something the officer could not see. And also the boy's face was terrified, a mask of grief barely held together, the face of a child who had lost his only parent and was now being interrogated by men who could ruin what was left of his life. Both expressions were there, layered on top of each other like two photographic plates exposed on the same negative. The officer saw one and then the other and then both at once, and he could not decide which was real, and he realized that the question itself was wrong. They were both real. The boy was both things at once.

We will be watching this lighthouse, the officer said. If there are any further reports of unusual activity, we will return.

You will find nothing, William said. And also you will find everything. You will find the truth you are looking for and the truth you are avoiding. You will find my father's research and my father's madness. You will find the creatures pulsing at four point seven hertz and you will find nothing but empty water. Both outcomes are true. Which one you perceive depends on which one you are capable of seeing.

The officers exchanged glances. They decided, simultaneously, that the boy was touched and that the boy was dangerous and that the boy was neither. They returned to their cutter and steamed away into the fog, and William watched them go from the gallery, his hand resting on the cold brass railing.

He went down to the kitchen. His father's body was there and was not there. The logbook was on the table, open to the page where Oliver Hartley had recorded the pulse frequency for the first time. Four point seven hertz. The rhythm of a human heart at rest. The creatures had matched it, his father wrote, and then they had drifted away from it, and then they had found it again. They were learning. They were communicating. They were something and nothing, real and not real, a discovery and a delusion, and Oliver Hartley had spent twelve years holding both truths in his mind without collapsing either one.

William understood now. His father had not gone mad. He had achieved a state of epistemic clarity that most people could not sustain. He had accepted that the world was superpositional, that truth was not singular, that reality did not resolve itself into one thing or the other. The creatures were real and unreal. The Navy had conspired and had not. He was dead and he was alive. All of these statements were accurate, and the effort of holding them all at once was what had kept Oliver Hartley standing on this rock for twelve years.

William took up his father's pen. He opened a fresh page in the logbook. He wrote: My father, Oliver Hartley, died of fever on the second of March, 1875. And also: My father, Oliver Hartley, speaks to me every night from the chair by the stove. And also: Neither of these statements is entirely true. And also: Both of them are.

He closed the logbook and placed it on the shelf behind the kitchen door. He checked the oil level in the lamp. He wound the clockwork mechanism. He went up to the gallery and stood at the railing and looked out at the sea, which was and was not empty, which held and did not hold creatures pulsing at four point seven hertz, which was and was not the last thing his father saw before the fever took him.

The light burned on. The superposition held. And William Hartley, fourteen years old, keeper of the light and keeper of the wave function, waited for the fog to clear and the truth to resolve and also accepted that it might never resolve, that this was the resolution, that holding both truths without collapse was the only way to be faithful to what his father had been and what he had seen and what he had tried to tell the world.

The last light on the Cornish coast burned on. And somewhere in the deep trench beyond the rock, or perhaps nowhere at all, the creatures pulsed at four point seven hertz, matching William's heartbeat, then drifting away, then finding it again.