Even my father appeared to sense the mass of the island. What approaches? he asked of no one—and indeed, the island was approaching us, rather than the reverse. Around midday, I made him and the doctor a small meal of biscuit and some pickled cabbage, with tea. The doctor looked up gratefully from his work and I pointed out that I was getting food for my father anyway.

By four, the island towered above us. Rodondo, Argyle said, named for an island in the Caribbean—at precisely the opposite point on the globe—which looked identical. The doctor concurred: it was not uncommon, he explained, for physical features on the earth’s surface to be exactly mirrored in another hemisphere. Such equal distributions of mass kept the rotation of planetary bodies in perfect balance: thus an ocean might counterweight a continent.

I had no idea whether he was right, but I wasn’t willing to take this at face value. ‘Is there a boat such as ours, then, sailing about the northern hemisphere?’

He looked at me with absolute sincerity. ‘I hope there is no other boat engaged in such sad inquiry as ours, miss.’

And damn him, just like that I felt ashamed to have been so flippant.

At five, the sun had fallen below the pinnacle of the island’s mount. The temperature fell rapidly, and with the prickling of my skin I felt the first stirrings of fear. I stayed near my father, though he was already insensible. Argyle worked the Moonbird around into the lee of the cliffs. The breeze had died to almost nothing by now, a quarter mile off the south-western slopes, but he was careful.

At the bow, the Connollys carried out a sounding. No sooner had they called forty fathoms than there was trouble: Angus had snarled his hand in the line and he lashed out in pain, caught Declan by the shirt and pushed him against the windlass. Declan grabbed him by the face and squeezed hard: ‘Fuck brother, will ye calm down.’ The Scotsman’s features were distorted by the iron grip, and foul curses leaked out one side of his squashed mouth.

The doctor wove between them, unworried. He was picking tiny crabs off the sounding line and scooping them into one of his jars, where the fluid immediately stunned them motionless and they drifted to the bottom. He was so absorbed in his work that he did not see me watching him. At such moments, I had noticed, the men forgot themselves. Engrossed by their work, or their arguments, their careful observance of a woman’s presence on board fell away.

‘Aagh me fuckin hand,’ sobbed Angus. His brother had stood away now, looked wearily up into the rigging.

But over the sounds of shipboard life I thought I heard other noises.