“I can’t!”

“Course you can. You’re brilliant.” Finn made a cradle from his fingers. “Put your foot in here. That’s it. Now reach up. Can you feel the way in?”

“I can’t do this.” She grabbed onto the rough rock with panicked fingers and wriggled in up to her waist. “I can’t do this, I won’t fit, I’ll get stuck.”

“You will fit and you won’t get stuck. Look at you, you’re built like a racing snake.”

Alicia inched upwards, fighting claustrophobia.

“Keep going, that’s it. Hey, did I tell you about the time I went potholing and nearly – actually, no, that’s a terrible story. Did you know about the post-box in town that doesn’t work?”

“What?”

“Keep going, that’s it – whoa!”

“What’s happening? Are you all right?”

“I’m fine, don’t worry. Just the sea trying to wash me away. Right, I’m coming up behind you, so whatever you do, don’t slip. Keep going, don’t freeze up. That’s it.”

“It’s so dark.”

“Shut your eyes and pretend it’s only dark because you’re not looking. So, you know the post-box that’s built into the wall just down from the church?”

A sliver of rock sliced her finger like glass. A warm trickle ran down her hand. “Yes, I know it.”

“Well, it doesn’t work.”

“What?”

“If you post letters in it,” said Finn, from somewhere below her, “it doesn’t work.”

“I’m stuck, I can’t, I’m slipping.”

“Don’t panic. Ask me how I know.”

“I can’t do this. I’m sorry.”

“You can, I swear you can. Come on, keep going. Ask me how I know.”

Alicia clawed at the rock, managed another tortuous few inches. “How do you know?”

“We were at the church fete,” said Finn. His breathing was ragged and the sound of the waves was like a giant wet mouth. “Ava and me, I mean. You know how sometimes you just – Christ, I think someone’s been sharpening these rocks – just end up at these things. How are you doing?”

“My hands hurt.”

“I know, mine too. Think of the amazing scars we’ll have. So, we had about ten pence each, so we bought some crap yellowy postcards from one of the stalls because that was about all we could afford. And the woman who had the stall said, Don’t post those in the letter-box in the wall outside. It doesn’t work. Don’t stop, you’re doing great, keep going. The higher we go the safer we are.”

“I’m scared.”

“Don’t think about it. Ask me a question.”

“Why did she think the post-box didn’t work?”

“That’s a great question. Unfortunately I don’t know the answer. We both just took it for granted she was telling… ” the sound of something falling “… it’s all right, we didn’t need that anyway… telling the truth. I mean, we were in a church, and she was a grown up.”

“Can we stop here? Please. I can’t go any higher.”

“I think we might need to.”

“Is the water still rising?”