Felix went on to relate how the sailor boy found a sealskin on the rocks nearby and, while the beautiful creature was distracted, hid it away under the decking of his boat. Then he took the woman home with him, not back to his mother and three sisters, who would likely have been less than impressed, but to a little hut by the sea. And there they lived for some while. He was happy enough, wed to the loveliest woman anyone in those parts had seen in a lifetime. But she pined. She wandered the shore; she tossed and turned by night; she was always searching for what had been stolen from her.

As the story unfolded verse by verse, there was a gradual lightening of the gloom around us. The water in the tunnel was higher. The creature made a sloshing sound as it waded on. My mind was on Gull’s description of the monstrous current that had caught him and Felix, sweeping them far up the underground passage. I put my cheek down against the sea beast’s hide, closing my eyes. You are strong. You are brave. I know you will keep us safe. The deep humming continued; I took it as a good sign.

Felix’s ballad drew toward its close. A wise woman from the local village helped the selkie to search for her skin, and they found it hidden under a pile of fishing nets. As the passage lightened around us, and the sound of lapping water could be heard ahead, Felix sang the final verse:

She slipped into the silvery skin
A seal once more was she
She dived into the briny depths
Joyous and strong and free.

Before we could draw breath for one last refrain, the creature threw back its head and roared. This was no sound of challenge, no trumpeting of war. It was a shout of triumph. Before us opened the mouth of the tunnel, and beyond it was the water of the bay, and the night sky overhead, and the moon sailing high, full and cool and lustrous.

“Hold on tight!” ordered Cathal.

Water was surging in on either side of us now as the tunnel broadened. The tide was rising fast. An image came to me, of the creature leaping forward and diving into the depths, as the selkie in the ballad had done, and of the human passengers being thrown hither and thither to be tumbled in the wild flow or pulverized on the rocks. But no. He would not do that. We were carrying Svala’s skin.

Before, the creature had edged sideways so we could step onto his back. Now he made a bridge of his neck and head, laying his chin on a rock shelf to one side of the passage entry. If we were bold and kept our balance, we could walk across to safety. From here, the moonlight would allow us to make a way around the bay to the place where Gareth and the others waited.