It turned out to be an extremely noisy island. Michaelmas Cay was a protected bird sanctuary. Not even Joh Bjelke-Petersen would have found it easy to get permission to build a five-star resort on this speck of real estate. You had to leave those birds alone. But nobody had contrived a way of protecting them from one another. They fought and screamed and exhibited all the other symptoms of paranoid anxiety that you expect of nature when it’s left to itself. Except of course that it wasn’t entirely left to itself, because we were there. Not that I was anything to fear. I scarcely moved. Every now and then I looked up to make sure that I could still see Ros’s snorkel, then I dropped back down again. It was bliss having so much space to myself. Ever since Townsville Rosalin and I had been getting fractious and clumsy, walking into each other, talking at the same time, answering, ‘Just look at that’, with, ‘Yes, but look at this.’ A few hours doing nothing on my own on a coral island, not looking at anything, was just what I needed, let the monotonous seabirds – terns or whatever – shriek all they like.

On the boat back to Cairns Ros was all excitement about the fish she’d swum with. She’d made friends with eels and a sting ray. She’d rubbed noses with baby sharks. She’d even cheered up a Depressed Gorgonian Crab. One of our diving instructors, Paul, joined in our conversation. I gathered that he was something else Ros had played with in the water. But he wanted to caution her against too relaxed an attitude to the deep. ‘The sea is no respecter of persons,’ he warned. (Now there were two of us sounding like David Attenborough.) ‘The sea is unforgiving.’

He was handsome, in an innocent, soldierly sort of way, with golden hair and a trim moustache; but so similar to all the other diving instructors we’d come across today that I wondered whether, like the fungia acitiniformis and the staghorn coral, he wasn’t yet one more miracle of polyp engineering. He claimed more conventional origins himself. New South Wales he told us he came from, and he had been in Cairns only six months. ‘Though I don’t expect ever to leave. Where else is there?’

None the less he still continued to harp on his theme of the dangerousness of the Reef. ‘Your worst enemy can be yourself,’ he said. ‘Panic kills more people than sharks do. You must never panic – or at least, if you do, you must recognize it for panic. Say “OK, this is panic. I’ll give it five seconds.” Then you say, “Right, Paul, that’s it. Panic over.”’

‘Right, Paul, that’s it. Panic over,’ I repeated, to show that I had got the hang of it.

‘That’s it. Except that you wouldn’t say Paul, you’d say—’