He buried his face into her waist and she stroked his head.

‘Robert?’

He spoke into Kathryn’s stomach. ‘I like it.’

‘Whatever can you like about a toilet?’

He didn’t reply.

‘Why don’t we sit down for a minute?’ suggested Kathryn.

‘But we’re going to Brownsea.’

‘There’s no rush, Howard.’ She led Robert over to the ledge of cushions beneath the window and sat him on her lap. He was wearing his T-shirt with a picture of the power station on the front. I’d bought that for him at the last open day. The picture had cracks running through it from so many washes; the towers were beginning to fade.

I stood at the window, the picnic bag still in my hand. ‘You had us worried.’

‘He’s sorry,’ said Kathryn.

Robert’s knees were pale and smooth, unnaturally so for a boy of that age, I thought. I was sure I’d had scabs and grazes at four, although I didn’t remember how I got them. I just remembered the pleasure of peeling back the congealed flap of blood, uncovering the fresh pink flesh beneath. ‘Don’t pick at it or it will never heal,’ Mum would say, offering a thick fabric plaster.

‘It’s all right,’ I said. I reached into the picnic bag and searched for a caramel wafer. ‘Is the toilet really your favourite room?’ I asked, handing him the wafer.

He nodded. I put the picnic bag down and knelt before him, placing my hands evenly on his knees.

‘Why is that?’

He shifted on his mother’s lap.

‘Robert? I’d really like to know.’

‘It’s got a lock on the door,’ he answered, biting into his biscuit.

It must have been around eleven by the time we boarded the ferry, and Robert had let go of his mother’s hand. The ramp clanked into place and grey smoke pumped out over the water. Kathryn said she would go and sit indoors, out of the sun. Gulls barked overhead and the salt in the air misted my sunglasses. I took them off and, squinting in the bright light, looked around for Robert.

He was sitting on deck with another boy. The boy wore a pair of red shorts, and his bare chest was darkly tanned, but he was smaller than Robert. He’d emptied a blue plastic bucket onto the wooden boards and they leant together, counting shells, their fingers sorting through the ridged lips. I remembered a shell I’d kept as a boy, how it had glinted on the beach, and how dull it had looked on the shelf back home.

‘Can I have a look?’

Neither one spoke.

‘Here.’ Kneeling by the bucket, I picked up a large mollusc. It was the wrong shape, but I held it to my ear anyway, tilting my head and closing my eyes.

‘Daddy – ’

‘Shush. I’m listening.’

The two boys looked at each other, Robert screwing his face up against the sun.

Reaching over to shield my son’s eyes, I said, ‘I can hear the sea. In this shell.’