‘Near enough.’ He jerked his head at the boat immediately in front of us. ‘That old tub will lag behind. Sails like a pregnant pig, she does, but near enough, near enough.’

Nimue’s horsemen waited for us on a spit of land that lay where the river turned south towards the sea. As we came closer she rode out from the mass of spearmen and urged her horse into the shallow water, and as we came closer still I saw two of her spearmen drag a captive into the shallows beside her.

At first I thought it must be one of our men taken from the stranded boat, but then I saw that the prisoner was Merlin. His beard had been cut off and his unkempt white hair blew ragged in the rising wind as he stared blindly towards us, but I could have sworn that he was smiling. I could not see his face clearly, for the distance was too great, but I do swear he was smiling as he was pulled into the small waves. He knew what was about to happen.

Then, suddenly, so did I, and there was nothing I could do to prevent it.

Nimue had been carried from this sea as a child. She had been captured in Demetia by a band of slave-raiders, then brought across the Severn Sea to Dumnonia, but on the voyage a storm rose and all the raiders’ ships were sunk. The crews and their captives drowned, all but for Nimue who had come safe from the sea onto Ynys Wair’s rocky shore and Merlin, rescuing the child, had called her Vivien because she was so plainly beloved by Manawydan, the sea God, and Vivien is a name that belongs to Manawydan. Nimue, being cross-grained, had ever refused to use the name, but I remembered it now, and I remembered that Manawydan loved her, and I knew she was about to use the God’s help to work a great curse on us.

‘What is she doing?’ Arthur asked.

‘Don’t watch, Lord,’ I said.

The two spearmen had waded back to shore, leaving the blinded Merlin alone beside Nimue’s horse. He made no attempt to escape. He just stood there, his hair streaming white, while Nimue drew a knife from her sword belt. It was the Knife of Laufrodedd.

‘No!’ Arthur shouted, but the wind carried his protest back in our boat’s path, back across the marshes and the reeds, back to nowhere. ‘No!’ he called again.

Nimue pointed her Druid’s staff towards the west, raised her head to the skies and howled. Still Merlin did not move. Our fleet swept past them, each boat coming close to the shallows where Nimue’s horse stood before being snatched southwards as the crews hoisted their sails. Nimue waited until our flag-hung boat came near and then she lowered her head and gazed at us with her one eye. She was smiling, and so was Merlin. I was close enough to see clearly now, and he was still smiling as Nimue leaned down from her saddle with the knife. One hard stroke was all it needed.