Gruff sat by his bedroom window and waited for dawn, his old wetsuit tight beneath his jeans and jumper. Hywel lay on his feet, a furry toe-warmer. The poor old dog had been cowering silently in the hallway when Gruff got back to the farmhouse. Everyone else had slept through the noise, which was a relief, but Hywel must have not only heard the sound but sensed the strangeness of it, and it had scared him to his bones. Gruff fussed over him and let him upstairs onto his bed, which Hywel thought was a win.

Gruff himself had managed a grand total of one hour and forty-three minutes sleep. In the quiet time between moon and sun, anticipation had got the better of him. He dressed, fed the chickens, collected their eggs, brushed Hywel’s coat, gave him his breakfast, and returned to his bedroom window to watch and wait for the light. A text from Mat told him that she too was awake and impatient.

HURRY UP SUN!

At last it arrived, a burst of thick orange light in a blood-red sky.

‘Red sky in the morning, shepherd’s warning,’ Gruff murmured.

Hywel followed him downstairs and watched whilst Gruff wrote Dad and Nain a note – Fed chickens and Hywel. Back soon. Gruff patted Hywel goodbye, put the hammer in his rucksack and the rucksack on his back, and slipped out of the front door to find Mat standing just outside.

‘Hi,’ Gruff said, and they set off together for the beach.

‘How long till high tide?’ Mat whispered. Her voice sounded husky, her breathing heavy. Her raw new gills showed as dark slashes on her neck.

‘An hour and a half,’ Gruff said. He hoped it was enough time. He hadn’t wanted to go out on the stones at night, but had a horrible feeling that if the tide turned before they had accomplished their task, it would be too late.

By the time they reached the head of the beach, the sky seemed to be on fire. Great bands of red and orange, broken by thin streaks of dark cloud, blazed across the eastern sky as the sun crept up from behind the far-off lumps and bumps of mainland Wales.

Dry sand slipped into Gruff’s trainers as they walked down the beach. The tide was almost ten metres past the first Sleeper already, and still coming in. A high tide to match the low of the night before.

There was a difference in the Sleepers. Like the silence when a sound you have become used to stops. The wind dying. A boiler going out. A buzzing light bulb switching off.

‘They’re not calling,’ Mat said.

‘Yes.’ Gruff looked out along the length of the stones. ‘They’re not tempting.’

They took their clothes and trainers off, down to the wetsuits, and Gruff stuffed everything in his rucksack. They waded out to the first of the Sleepers.

Mat put her hand on the stone. ‘Oh … Gruff, touch it!’

Gruff placed his palm flat against the first Sleeper and contentment flooded through him, a feeling of rightness that twitched his mouth into a smile. ‘They’re happy,’ he said. ‘They’re all together again.’ Their hole of yearning was filled. No one would be lured into it now and swallowed by the sea. No more danger for Prem or Rosie or anyone else.

No more danger from the Sleepers, at any rate. Dylan was still out there, and a storm was on its way.

Mat climbed onto the first stone and Gruff followed her. They paused to dry their feet as much as possible with the towel Gruff had brought, and then put their trainers back on and set off along the Sleepers, Mat first. Beyond her, the brilliant orb of the sun cleared the horizon and spread dazzling light across the sea.

Mat already had the sword in her hand when Gruff joined her on the seventh Sleeper. She lay flat on her stomach, half hanging down towards the water. She raised the sword as he knelt beside her and the sun flashed on its turning, twisting hilt. ‘Ready?’ she asked. Her breathing rasped and Gruff saw with a jolt of unease that her eyes were steeped in leaping water.

The morning was very still. The sea was quiet, the wind little more than a sigh. Gruff was not sure if it was his own anticipation but the air seemed to thrum in his temples, in his veins. His sight seemed paper-thin, hyper-bright, everything in sharper focus than normal. He opened his rucksack and took the hammer from it. ‘Ready,’ he said.

Mat plunged the sword into the sea, withdrew it and plunged it in again. She counted quietly, ‘Raz, dwa, trzy, cztery, pięć, sześć, siedem.’ She eyed Gruff sideways and grinned, her ocean-filled gaze bright. ‘Polish.’

Gruff grinned back. He tightened his grip on the hammer and took a steadying breath.

Mat held the sword beneath the water with both hands. Gruff leant forward and brought the ancient stone hammer round and down, breaking through the surface of the water and finally, finally connecting with the blade. A pure, sweet note ricocheted through the sea and reverberated back up his arm to sing in his bones.

Mat laughed aloud.

Un,’ Gruff gasped, stopping himself from bouncing up and down for joy in case he fell off the stone. He withdrew the hammer and repeated the movement, and the note rang out again. ‘Dau.’ On he went, counting each blow as it fell. ‘Tri, pedwar, pump, chwech, saith.’

They were doing it. It was working.

Mat drew the sword out and thrust it down, counting again.

After its first blaze of glory, the sun was now scrambling up through thickening clouds. The wind grew. Gruff hardly noticed; he had eyes only for the hilt and the hammer and the lengthening, invisible blade. Before long he was counting in Polish and Mat was counting in Welsh and they were both giddy with hope and relief and laughter. The singing notes of hammer on blade wrapped them in a cocoon of sound that the outside world could not penetrate.

Mat tested the sword occasionally, padding along the flat of the blade to see how long it had become. ‘It’s narrowing,’ she said, each time. ‘Nearly there … we’ve got to be nearly there.’

Gruff struck the first blow of a set of seven and the same note rang out, but on the second a different, higher note came in harmony to the first, and on the third a deep, low note, a different one again. And on, until with the seventh blow the chord swelled around them, felt rather than heard: a chord that was almost out of harmony but holding itself together on a delicious edge of unresolved-resolved sound.

He sat back on his heels and put the hammer down, rubbing his tired arm. Mat pulled the sword up and out of the water – and the blade was there for anyone to see: long and sharp and wicked and beautiful, fluid and solid, keen and complete.

‘We did it,’ she whispered.

Gruff stretched one careful finger out to the blade. It was solid and dry to the touch, though it looked for all the world like flowing water.

The first drops of rain pattered to the sea around them and splashed on Gruff’s cheek. He snapped his head to the sky and only then did he see the broiling, purple-black clouds covering the sun; only then did he feel the hissing excitement of the wind.

He looked back to the sword and hoped against hope that they had done enough. ‘Here comes the storm.’