Eventually I stagger into the open cab and find David sitting at the steering wheel, peering at something through the dirty window. He sees me and looks surprised.

‘Tom’s feeling sick,’ I explain.

‘Oh. I was going to show him this.’

My legs are freezing cold and hopelessly weak. Not trusting them to hold me up, I drop onto the seat next to David. He points outside. One of the huge black birds is perched on the bow of the boat, facing out to sea. It turns to the side and its proud black chest shimmers with bronze scales that flash green and purple.

‘What is it, a cormorant?’ I ask.

David raises his eyebrows and nods, seemingly impressed. ‘Sea-ravens are what we call them. The Irish call them the cailleach dhubh – the black hag. Sinister-looking things if you ask me. I’ve seen plenty in my time, but never had one land on the boat before.’

The creature repositions its feet and spreads its massive black wings, hanging them open to dry like a broken umbrella. It makes a juddering, throaty sound almost as if it’s talking – then it turns to look straight at me and cackles.

I flinch but the bird has already gone – taken up into the clouds with a single, mighty flap of its wings. The boatman ducks his head and we watch through the window as more dark shapes appear in the sky.

‘That’s five, six. No, wait … eight of them. Well I’ll be.’

‘What’s that?’ I ask.

He strokes his moustache and sniffs. ‘There’s an old superstition that says the birds are witches. If you see nine of them in the sky at once, death is sure to follow.’

‘How cheerful.’

He laughs. ‘The island is full of stories. I don’t imagine King Arthur or Merlin is over there either, despite what some folks would have you believe.’

I think back to the research I did, remembering how some people think the place is Avalon. In the stories, King Arthur was taken by boat to an island shrouded in mist. Bardsey is the nearest island to where he fell in battle on the mainland, and there was something to do with Avalon meaning ‘Isle of Apples’ and Bardsey having its own species of apple tree. It all sounds a bit convenient; a way to bring in the tourists. But there were other things I read too.

‘Is it true about the saints?’ I ask.

David nods. ‘Aye, that’s right. Twenty thousand holy confessors and martyrs are buried on the island. Dig anywhere and you’ll find bones. Religious men have been making pilgrimages to the place since the fifth century; hundreds still do every summer. The land is said to be so holy that anyone who dies there goes to heaven. I can’t say if it’s true, though there have been plenty of ghost sightings over the years. I just know the place is special.’

I nod and make a mental note not to go digging. He peers at the sky through the window, and I count eight of the birds, flying so low I can see their long thin legs. It’s easy to imagine a group of witches above us, their wings fluttering like tattered black cloaks.