No one had expected twins. No Tremethyk had ever had twins before. Gran Bersaba blamed Pasco's wife. She was an outsider and had brought foreign blood to the Tremethyks. She'd distorted the way of things.

'Which one will be your Lutey now?' Gran Bersaba asked. 'You've none to offer the sea.'

Maria laughed at the old woman and pressed the babies to her breasts.

'You speak such nonsense,' she said – with fondness, though Gran Bersaba was offended nonetheless.

'You've no right to snigger at the traditions of a people older than the earth you were whelped on,' said Gran Bersaba. She looked at Maria with such coldness that for a moment Maria was afraid and she wondered if the stories were true after all. Had the mad old witch drowned her first born? Maria shook the thought. She only had to look at Pasco to know that those stories were just stories.

She bent down and took a deep breath, committing the warm smell of her children to memory.

'One of them will be called Lutey. Of course. It's Tremethyk tradition,' she said.

'Oh aye? And which will you choose? Which can you lose?' Gran Bersaba asked.

'Give over, Mam,' Pasco said and he leaned forwards and kissed one of the boys on the forehead. 'We're not losing anything.'

'Of course. You aren't losing anything. You know the future better than I ever could,' said Gran Bersaba and she walked out of the room.

*

Maria didn't see much of Gran Bersaba after that. The few times she had tried to take the boys up to see their grandmother something had always happened. A wheel came loose on the pram as she tried to take the path to Gran Bersaba's cottage. A rock fall made the path impassable one summer. The one time Maria had got close with her boys, a dog had come at them, hackles raised and teeth bared. She wondered again if the rumours about that the old woman were true. Could she have spelled Maria away from her home?

But again, Maria shook her thoughts away. Pasco never had a problem getting to his mother. He visited her once every few months and came back shaking his head and smiling gently.

'That woman,' he'd say. 'Madder than a box of frogs!' It was clear how much he loved her.

The boys, Lutey and Santo, were always curious about their grandmother, but they never asked to go with their father to meet her. Instead, they begged him for stories about her. She grew big in their imaginations.

Lutey and Santo were identical. They looked like Pasco, though they had their mother's eyes, brown and earthy.

'Grounding eyes,' Pasco would say. 'They'll keep you on the shore.'

All the same, Pasco taught the boys to swim, sail, and fish before they were ready for school. Those boys were no strangers to the sea. They were water babies and Maria loved to go down to the beach with them. On hot summer's days, when they were still small, she would set them in a rock pool and watch them splash and squeal with delight, discovering a small sample of the world just lapping at their side.

When the twins got bigger, the whole family would take the boat out and swim in the deeps. Maria would joke that they were all growing gills.

As the boys grew older they grew different, but they were close. Lutey was an artist. He painted and sang and made love to the world; a Delgado in every respect. Santo was a healer, like every Tremethyk that had come before him. It wasn't long before Lutey was breaking hearts and Santo was mending bones. And as Lutey learned how to create pieces of beauty at his mother's side, Santo learned everything he could from his father at the clinic.

But not everyone came to the clinic for help. Some people chose to visit Gran Bersaba for what Pasco called ‘mendings’.

'What kind of mendings?' Santo wanted to know.

'Mendings of the heart and the head. Of the soul,' Pasco told him.

'How can she mend those things?'

Maria laughed then.

'Go and ask her, Santorini!'

'Maybe I will,' he said, smiling. His mother smiled back at him, but he could see she was worried.

Maybe I will, he said to himself.

*

When Lutey and Santo met Gran Bersaba it was the middle of winter. Santo woke early and suddenly knew that it was time. He shook Lutey awake and they left the house and found their way down the small track that led to their grandmother's cottage.

She was waiting for them.

'So, you've finally come, have you?'

'Nope,' Lutey said cheerfully.

Gran Bersaba looked at him with hard, hawkish eyes. It was a penetrating look; the kind that left you feeling like you had no secrets. And when she finally looked away it felt as though she had been holding him the entire time and now she was letting him go.

'Come in. I'll get some tea on. We've much to talk about,' she said, disappearing inside. The boys followed her.

They walked right into the kitchen; a round room with a low ceiling. The walls were whitewashed. A large table stood at the centre and a fire burnt in a hearth just beyond it. Herbs, flowers, odds and ends, hung down from a wooden rack above them. The room smelt of smoking peat, gorse and honey. The boys felt at home immediately – it was one of those sorts of rooms – and they sat down at the table and watched Gran Bersaba as she filled a pot with hot water from the fire. Then she sat down and looked them over.

'Well, you look like Tremethyks right enough,' she said. 'What's Pasco told you of your heritage?'

Lutey grinned. He loved the stories.

'He told us about Lutey of Cury and the mermaid,' he said. 'The deal that was made and the traditions since.'

'Did he tell you about his brother?'

Lutey and Santo frowned at her.

'He never said he had a brother.'

'Oh aye. Just like him I suppose. Pasco and Lutey weren't close. Lutey wasn't a kind boy. He could be harsh with Pasco. But he was his brother all the same and Pasco took it hard when he was gone.'

'How did he... go?' asked Santo.

'He was called Lutey too?' said Lutey at the same time.

'Aye. There's a Lutey in every generation of Tremethyks. And as for how he went... the same way your Lutey of Cury went of course. The mermaids took him.'

Santo assumed this was Gran Bersaba's poetic way of saying he had drowned. Lutey thought she was mad and really believed what she was saying. Both of them were suddenly sad as they thought of their father being told he would never see his brother again. And at that moment Lutey took Santo's hand and squeezed it.

'Of course, many'll tell you I drowned him. They say I did it to appease the Sea. People were so sure of it back when he disappeared that the police even arrested me. But there was no proof they could find. There was nothing to be found. As if it wasn't painful enough to lose my firstborn? They had to blame me for it too. People said some wicked wicked things.

'But they never stopped coming to me for mendings. No. They might have been frightened of me but when it comes down to it, people will do anything they can to help themselves.'

Santo wanted to ask Gran Bersaba more about her mendings but Lutey spoke first:

'How did it happen?' he asked.

Gran Bersaba looked him over, as if she were weighing his value – was he worth her story? Then she nodded to herself and poured out the tea into three big mugs.

'Here. Have a spot of tea and listen.'

The boys sat back in their chairs and watched Gran Bersaba as she began her tale. Her skin was coarse and wrinkled and her face was hard with sadness. Her voice carried the sound of the gulls and her story floated them away.

'You know the first Lutey of Cury found a mermaid stranded in a rock pool. She was a devious little creature, and she damn near stole Lutey from his home then and there. But Lutey was a good man and a higher power was looking out for him that day. The mermaid took her loss with good grace and even granted Lutey five wishes, but these wishes weren’t without consequences. In order to enjoy his wishes, and live at peace with the Sea, Lutey had to make a deal: to return to the mermaid in nine years. And not only that. His descendants would have to honour the deal too.

'Lutey went to her willingly on the last day of the eighth year. And as he sank into the water the deal he had made became more than the words he had uttered. It became part of his family. Every nine years a Tremethyk would give himself to the Sea, and not just any Tremethyk: always a Lutey.

'The Sea honoured the deal, as did the Tremethyks. Every generation, a Lutey was born and they were taken on the eve of nine years. But then suddenly they weren't taken. No one knew why, but Luteys stopped disappearing. The Tremethyks thought little about it. Old Lutey of Cury was passing into legend; the missing were becoming coincidences. Nevertheless, every first born Tremethyk boy still bore the name of Lutey, for the sake of tradition.

'I grew up not far from here and I knew Lutey and Ruan Tremethyk very well. There was never a pair so handsome in all of Cornwall; hearts just sang when they saw them. I imagine it's much the like for the two of you.' Gran Bersaba gave the boys a knowing look. 'Well, I fell in love with Ruan and I was lucky to catch his fancy. He married me and we settled into a cottage in town. Lutey lived here, in the Tremethyk home. But he wasn't satisfied with life here and for the first time in Tremethyk history, a Lutey left Cornwall. He moved to London and got himself a job in an office.

'Ruan and I took over this house. At first, Lutey visited often, but as the years passed his visits grew less frequent. The last time he came he spoke to me. He said: I cannot bear the call. She sings deep inside me and I'm terrified to answer. Who, I asked, Who? He looked at me, but it wasn't me he was seeing. The mermaid, he said.

'After that, he went back to London and never came back. I didn't think much of it at the time. I didn't think much of Lutey. In fact, I forgot all about the incident until many years later.

'Ruan had taken the boys out fishing. Pasco had caught nothing but Lutey wasn't making fun of him for it. Instead, the boy looked thoughtful. I gave him a penny and Lutey looked at me and said: "She's singing deeper now. It's almost time to go."

'My boy Lutey disappeared a year later. We were working on the shore, mending nets and enjoying the sunshine. I wasn't watching the boys; they knew their way around the coves. But I knew when Lutey was gone. Suddenly I knew. I looked for him along the water's edge but he was gone. And Pasco was standing there watching the water. Of course, I couldn’t get any sense out of Pasco about what had happened, but I knew the truth in my heart. The Sea wasn't finished with the Tremethyks. It had just forgotten for a little while.

'Of course now you two boys are here, and one of you a Lutey.' Gran Bersaba nodded at Lutey. 'But you're twins. It's always been the first born that's been a Lutey, but they jumbled you two up. Who knows if the right one bears the name? Who knows if twins can be separated? Who knows if the Sea will even remember you? Things changed when Pasco chose your mother. Things are different now.

'I've given Maria a hard time, it's true, but perhaps she was the best choice Pasco could have made. Perhaps things will be different.' Gran Bersaba sighed. She looked at the boys for a moment and then stood up. 'Right then. That's my story. That's what I give to you, Lutey. And Santo, you have a wish to know my mendings?'

Santo nodded at her.

'Come on Saturdays. Seven o'clock. Don't be late. I'll teach you what I know.'

*

Maria wasn't thrilled by the thought of Santo spending so much time with Gran Bersaba, but she could see his thirst to know things, to understand more than he did. Lutey took it upon himself to go with Santo every weekend; the Tremethyk house was in a picturesque spot and Lutey enjoyed painting the sea.

After some months, Lutey arrived to find an easel waiting for him.

'So you can work on a bigger scale,' Gran Bersaba said, and she disappeared before he said thank you. Lutey would listen as Gran Bersaba told Santo all about the healing properties of the world around them. He enjoyed the folklore she passed on with her knowledge. But some things were secret and for Santo only.

Then there came a day when Gran Bersaba drew both of the boys together and sat them down, much as they had sat the first time they had met her.

'I've passed on all I know. The stories, the knowledge, the history of this place. My work with you is done. It's time you went your own ways. You're men now. Tremethyks. Delgados. Use your gifts and try to make the world you know the best one it can be.'

Gran Bersaba stood up and turned her back on the boys. Lutey wanted to protest, he wasn't ready to say goodbye, but Santo pulled him by the arm and dragged him out of the house.

'It's time,' Santo said and when Lutey looked at him he knew Santo understood more than he did.

'What do you know?' he asked. 'What is it?'

Santo shook his head.

'I'll tell you soon. Let's go though. It's time to go.' Santo slung an arm across Lutey's shoulder and the pair of them walked away.

Santo persuaded Lutey to come out in the boat with him that afternoon.

'We haven't been fishing in a while,' Santo said. It was true and they always felt better on the water.

They took out Pasco's old boat, and motored a long way from the shore, out to the deep, where they laid anchor and dropped their lines. For a while they sat in silence. And then Lutey asked:

'What do you know?'

'Gran Bersaba is moving on tonight. She told me it was time. She's passed on everything she knows. She's tired. I think she just wants some peace, now.'

Lutey wasn't sure he quite understood Santo's words.

'How can she just...move on? She's not killing herself, is she?'

'God no,' Santo said. 'She wouldn't do that. She just said she felt it in her bones. She wants to rest.'

'Why did she tell you? Why didn't she tell me herself? Doesn't she trust me?'

'She trusts you; of course she trusts you. She just thought... you know how different we are, Lutey. I think she just thought I would handle it better. She thought I would break it better.'

Lutey dashed a hand into the water. He wanted to shout at Santo but he knew it wasn't his brother's fault. He kept quiet and the two of them sat, rocking gently from side to side as the water swelled beneath them.

'I know I wasn't as close to her as you, but Gran is... she's special. I feel like I won't know which way to go without her.'

Santo stretched across the boat and took Lutey in his arms.

'I know. I feel the same way. I–'

But Santo never finished what he was going to say. He froze where he was and felt Lutey go dead in his arms. They both stopped breathing and listened. There, under the cry of the gulls and the soft lap of water against the hull, was a voice. It moved through water and air with a languid motion, a whisper, mellifluous and almost tangible. Almost a taste. They felt it in their mouths, in their stomachs, in their hearts. It worked its way deeper into them, like water filling empty vessels, until they were all full up with song and they broke apart and gazed down into the water.

The water was clear, green and cold. It was so deep they could only see darkness down below that layer of green. And then a shape seemed to gather out of the darkness, light shifting across it as though it was dancing across a mirror. The shape grew larger, not quite making sense at first, but then resolving itself into an image of dreams and stories and their past and present.

She broke through the surface of the water and, after the sound of her song, the lapping water sounded as brittle as breaking glass. Shaking back a mane of dark hair, she gazed at them and they gazed back at her.

She wasn't like they had imagined. Her tail was black, dappled with clouds of silver, and it melted into skin just as dark. Her nose was wide, and her nostrils were slits that closed against the water. She had a high forehead. Her face was dominated by large liquid eyes, black as a seal's. And her lips... her lips were fine. She smiled at the boys and they saw her sharp teeth and her white tongue. She was the most beautiful thing they had ever seen.

'Lutey?' she asked.

'Yes,' Lutey and Santo said together.

The mermaid looked from one to the other and a frown wrinkled her lovely brow.

'I can take only one. I can take only Lutey.'

Lutey leaned forward and touched the water with his hand. As his fingers dipped under the surface the song that had stretched through him, broke into pieces and he was suddenly overcome by a black fear.

'Not me,' he whispered. 'No. Not me.' But as he tried to draw away from the water the mermaid took his hand. Her own was cold and rough with scales, the fingers were webbed and she had talons for nails. She gripped him hard, squeezing the blood from his hand and Lutey cried out with pain and fear.

'No!' he cried. 'It isn't me! I'm not Lutey!'

Santo stretched forwards and tried to take the mermaid's arm, but her skin was slick and he couldn't hold her.

'Take me!' he said. 'I'm the one you seek!'

The mermaid looked at him, her eyes narrowing in consideration.

'You're one and the same. One is as good as the other, and you weren't named Lutey on your birthday.'

'There was a mistake,' Santo said, his words tripping over themselves as he took his brother by the arm and tried to pull him back into the boat. 'They mixed us up. I'm the one you want.'

The mermaid laughed, a deep hollow sound, like breath being blown through a conch.

'Too bad, too late, it's your mother's mistake. It's been nine years. Time to take what's mine.'

She pulled Lutey from the boat and dragged him down.

'NO!' Santo cried. He flung himself into the water and tried to follow his brother down into the deep. Through the blur of water he saw Lutey struggle and fight, but there was nothing he could do against the strength of the mermaid and Santo couldn't reach him. He fought his way through the water, tried to get deeper, but it was pushing him back and it was stronger than he was, and as his chest tightened, his will weakened and he floated back to the surface, all the while looking down, watching the darkness that had swallowed his brother. The image of Lutey’s struggle played and replayed in his head until all Santo could see was himself, drowning.

Finally, he hauled himself back into the boat and lay in its bed, dripping water and sorrow. The song was thick around him. The mermaid had taken the wrong Tremethyk and Santo sensed this was the end. No more Luteys would be lost at sea; his brother had been the last. It was a high price to pay. Santo cried until he fell asleep and then he dreamed of the world Lutey had been dragged down to. The world that he, Santo, was meant to be a part of.