The brothers were bickering. About seals this time, as we passed by Curtis and its grim neighbour, the Devil’s Tower. The formation opened into two separate spikes as we drew nearer, bald granite spearing vertically from the waves. I could see, even at our wide clearance, that the rocks were a haul-out for seals. The swell washed heavy and blue over the weedy foot of the towers. I had by now become accustomed to the streaks of seal excrement, bleached in the elements, and the pungent smell of their bodies when the wind offered it our way.

‘Stromness…’ I heard. ‘On the Scapa Flow.’ It was Angus, a dreamy smile. ‘Grey seals, right? But these uns are red…’

Declan grabbed his brother in a half-hearted headlock and started up a string of insults about selkie-folk. Angus punched lazily at his brother’s shoulder. ‘They’s not seals. Seals’re grey, can’t fool me. An they got no ears.’

‘So what’re these then, feckin elephants?’

‘Master’ll know,’ said Angus, as though bringing Argyle in would resolve the argument.

Declan only laughed. ‘Him? Old Man o’ Hoy in a dress?’

‘Language.’ Argyle scowled at them, an eye to me. The scowl had the desired effect: they hadn’t intended for him to overhear. ‘They’re seals, but of a particular kind,’ came the doctor’s voice from his favourite spot against the cabin wall. ‘Pinnipeds. It means they have ears.’

As we left the tower of rock and the seals behind, the low sky over the ocean ahead filled with drifting black mists. Birds, millions of them, small and dark. We’d seen them over the water already, impossible to count in their swirling abundance, impossible to track an individual by eye. More like insect clouds than aggregations of feathers and beating hearts.

The Moonbird ploughed closer and closer to the great flock, and now the cloud of birds was parting, allowing the boat passage through the mass. They whipped past the rigging, darting and bending and making corners in the air. I could smell their bodies, distinct from the mineral sea and the lingering scent of the seals, life in those weeks being the exchange of one stink for another.

The doctor had rushed below decks and emerged again with a knife and a handful of fish, running the blade along them so their innards spilled and hung. He twisted the opened fish into a sheet of his fine netting. This he roped off with cord and slung overboard; a bouquet garni for the sea. He held the cord with one hand, and in the other waited a dip-net on a long pole. The great avian cloud formed a finger that pointed to the waiting bait: a cluster of birds circled in and stabbed at the gutted fish. The doctor pounced, swinging the pole down and the net caught a bird in the act of swallowing.