I heard a heavy crash. I thought it was us, but there was no movement to suggest it. The sound must have come from ashore. Voices, laughing then silent. Who would laugh, here and now? And why did they not continue? Why was there no conversation? I was profoundly confused. The timber where I rested my hand—I was clinging to the base of the gaff—was slick with moisture.

The silence cracked a little once again, this time to reveal song. A man’s voice, thick as tar through deep notes, then failing at its upper registers. The words unclear, the final line cracking hoarse, then silence.

I wanted to be gone.

I could not see the end of the bow from where I stood amidships. Still the damned whiteness. No sound for a long time, the boat creeping forward in the gloom. Over shallower water I felt more conscious of its lifting and yawing. I could not remember discussing why we were doing this. Why were we here?

Another crash and this time a scream. Pain, not fright. I could smell plants now, wet seaweed and guano. More sounds that could have been laughter. The spaces between sounds were too long, and their disconnection made them more unsettling.

Dr Gideon was on the deck, drying his hands on a cloth. He hung his head down, listening intently. The small wake of the Moonbird could be heard now, lapping on the unseen shore. The air was so still, the sea so oily, that these mere ripples rushed like unimpeded surf.

‘You’re looking out the wrong side,’ he said quietly.

‘It’s plainly there,’ I said, and pointed directly towards the noises.

‘Fog refracts it,’ he countered. ‘It’s off the other quarter.’ He crossed to the far side. I followed him; he seemed certain, and as I did so the air moved and the light changed. More water appeared at our side, inky first then fading to paler green and I saw with sudden alarm that we were very close off the boulders; so close that I could make out shapes on the bottom in the clear water.

‘Draft?’ asked the doctor, an eyebrow inclined towards the master.

‘Nine foot.’

We were using every inch of it. The lesson of those soundings was that nothing beneath us would happen in a gradient. The four fathoms could vanish and we would strike a boulder. They were everywhere: the previous day I’d seen Argyle weaving around them in what I thought was open water. In such calm seas, without whitewater on the surface to indicate their presence, they were even more dangerous.