As Simon followed Ned back across the lawn, an unease rippled through the party guests; you could see it. Parents corralled their children, some of the other guests had formed a barefoot search party. They walked around peering uselessly, holding sodden paper plates and going no further than the garden’s edge.

Simon thought he caught sight of Audrey’s white skirt. He followed her around the corner of the house, and found her by a cardboard cubby-house. ‘Audrey—’

She turned to look at him. Her eyes fat with tears, her mouth a red, sad line. She had ripped off the cubby-house door, held it in her hand. Simon could see the interior held no more clues than a used dinner plate, some comics and a plastic sword.

‘He’s gone,’ said Audrey. ‘Gin’s gone.’ She handed Simon the door.

‘He can’t be far.’ Simon set the piece of cardboard down. ‘Have you checked the house, places he likes to hide?’

She nodded. ‘He wouldn’t just run away on his birthday. He’s been talking about it for months. And we haven’t even had the cake.’ She started to sob.

Simon thought about what Megan had said about Audrey. After her mother…the sadness. ‘Wait,’ he said.

‘What?’ Audrey tried to dry her face with her sleeves.

‘Audrey, when…your mum—’

‘No!’ She slapped Simon on the arm so it stung. ‘Shut up about my mum! She’s got nothing to do with this!’

‘No,’ Simon tried to brush away her flailing arms. ‘No, where did she go?’

‘How the hell am I supposed to know? If I knew—’

‘I mean, where did she go missing? Whereabouts?’

Audrey went to hit him again but at the last second held her hand. ‘You think—’ and then she was off. Her feet exploded from the ground as she half-ducked half-slid under a low hanging tree at the edge of the garden and was gone. Simon ran after her. He crawled under the same tree and realised it covered a gap in the fence that led to a faint track through the scrub. Audrey was some way ahead, weaving through branches, legs pistoning, her canvas shoes pounding through the tussocky grass.

‘Audrey!’ With a grunt of frustration, Simon set off behind her, the whip-thin branches lashing his cheeks as he ran. His bare feet laboured in the soft sand and his breath soon spun in ragged spirals, but he kept his eyes on Audrey, never letting her out of his sight.

Just as she crested the top of a dune, her left foot caught an exposed tree root and she fell in a flash of white, tumbling onto her arms, her shoe flipping off behind her. Simon caught up to her as she struggled up.

‘Are you okay?’ he said.

‘Fine. Just my ankle. We’ve got to get—ow!’ She winced as she stood on her left leg. ‘The beach. By the bluff.’

‘That’s where Gin is?’

She nodded. ‘That’s where Mum went missing.’

Simon looked up. Beyond the dune was simply blue-grey sky, the death-drop of air that meant the end of land. He retrieved Audrey’s shoe and she slipped it back on.

‘This way,’ she said, limping to the top of the dune.

Simon joined her. The beach opened out below them, shimmering away in both directions. Ahead, the water was unsettled iron all the way to a storm-smudged horizon. A crisp human detail caught Simon’s eye: the white glint of a ship way out to sea. The bluff sat to their left, waves roiling at its base. It was sheer, scooped from the sand like a wave itself, a huge dark rock caught in an elemental wedge.

‘There!’ Audrey pointed to the bluff’s base, and Simon made out the flash of tinfoil. Gin’s helmet. The boy was a tiny speck on the sand.

‘Gin!’ Audrey shouted, but her voice was carried away. ‘Gin!’ Hands cupped at her mouth. Gin didn’t move. He was sitting among a collection of driftwood, swinging his legs back and forth. ‘Come on,’ said Audrey, grasping Simon’s hand. She led them carefully down the other side of the dune, stepping down sideways with careful steps.

Simon thought of Pony and the grandstand, stepping over the rotten seats. Audrey grimaced with every step as they half-slid to the bottom of the dune then began to jog towards her brother, dragging her left leg along with her. When they were close enough, she shouted again, and Gin lifted his head. Beneath his helmet, his cheeks had been stung pink by the wind. The piece of driftwood he was sitting on was enormous, and Simon realised it was part of a ship, eroded slices of hooped wood from a hull.

Audrey let out a loud sigh. She flopped down on her knees next to Gin and looked into his eyes. ‘Are you okay?’ she said. ‘Is everything all right?’

‘Yes,’ he said. ‘I just came to the beach, Audrey.’

‘I know you did. But you should have told me.’

Gin nodded solemnly. ‘I wanted to come alone.’

‘But it’s your birthday. There’s going to be cake soon. Don’t you want all your friends around you? And your family?’ She smoothed down creases on her brother’s shirt.

‘I came to see Mum,’ he said.

Audrey’s eyes had fresh tears. ‘Yes,’ she said. ‘You did, didn’t you.’ She struggled to her feet and sat next to Gin on the wood.

Simon stood a little distance away, unsure.

Gin waved at him. ‘Do you want to sit down, Simon? This is a ship, but you can sit on it.’

‘Okay,’ said Simon. ‘If that’s okay.’

‘It’s for everyone,’ said Gin. ‘It was my mum’s favourite spot, but everyone’s allowed to use it.’

Simon walked over and sat down next to Gin. Audrey stayed silent, staring out across the water.

‘My mum liked birthdays,’ said Gin. ‘She would make us something. From wood. Animals.’ Gin’s crinoline space-suit crackled as he moved.

‘Do you still have the animals?’ said Simon.

Gin nodded. ‘I keep them in my room, side by side.’

Audrey sniffed. Her voice came out quietly. ‘She’d tell us the sea made them. She’d say she’d found them on the shore.’ Simon looked over to see her smiling. ‘The same way the water washes rocks smooth. Million-to-ones, that’s what she’d say. The only pieces of wood in the world to have travelled just the right distance and touched just the right amount of water and salt and tumbled and turned in just the right way to come out looking like an animal.’

‘She made me a shark,’ said Gin, ‘last time. With teeth and everything. I told her sharks don’t come to the beach, because of the nets.’ He pointed out at the ocean, counted out the buoys with a bouncing finger. ‘She said baby sharks swim through the nets when they’re little and then they grow up and can’t get back out to sea. So she gave me it to look after.’

‘That’s sad,’ said Simon. He pictured sharks biting at the nets, trying to get back home. ‘It must be sad, coming here. To your mum’s favourite spot.’

‘We haven’t come back in a while,’ said Audrey. ‘Anyway, it’s not the saddest thing I know.’

‘What’s the saddest?’

‘The G minor chord.’

‘Like in music?’

Audrey nodded.

They both turned their heads: movement back down the beach. A pair of people were coming towards them, flickering shapes in the distance. Simon picked out the yellow flutter of a summer dress. Madaline and Ned, breaking into a run across the sand.