The lighthouse was called The Longing. Pitched amidst tessellations of rock black as coke, thrashed for over a hundred years by disconsolate squalls, it needled upward, spine-straight, a white bolt locking earth, sky, and ocean together. It was lovely in its decrepitude, feathery paint gnawed off by north winds and rust-blazed window frames signatures of use and purpose. I always thought lighthouses were beautiful symbols, but this one was more than that – it was hauntingly familiar.

Night was drawing in and we hadn’t yet met the owner. We’d driven hundreds of miles over mountains, through sleepy villages and along winding roads, usually behind herds of cattle. We had taken a ferry, and got lost four times, on account of using an outdated, coffee-stained A–Z road map with several pages missing.

I parked up behind an old Range Rover. ‘We’re here,’ I told the girls, who had fallen asleep against each other in the back. I wrapped my raincoat around Clover – she was wearing only a swimsuit over a pair of jeans – and lifted her up to walk a little way along the rocky beach daubed with spiky patches of marram and tough white flowers.

The four of us scanned the bay. It was a raw scene: a full moon hiding behind purple cloud, ocean thrashing against black cliffs. Gulls wheeling and shrieking above us. Trees stood like pitchforks, flayed by the wind. They hemmed the island, watching.

II

The lighthouse keeper’s bothy was a squat stone dwelling built close to the lighthouse. Smoke plumed from the chimney, pressing the earthy smell of peat into our noses. A woman stepped out to greet us. ‘Olivia?’ she said.

‘Hi,’ I said. ‘Sorry I’m earlier than expected …’

‘No trouble at all. Come on in out of the cold.’

We found ourselves in a cramped hallway, where someone had pinned a shark’s jawbone to the inner wall. Luna reached out to touch one of the teeth and I tugged her back.

Saffy nodded at it. ‘Is that from a great white?’

‘Porbeagle shark,’ the woman – Isla – said with a tilt of her chin. ‘We don’t get great whites. Porbeagles are just as big, mind, and every bit as dangerous.’

‘I don’t like sharks, Mummy,’ Clover whispered.

‘We have a basking shark that tends to hang around the bay,’ Isla said. She glanced down at Luna, who threw me a panicked look. ‘You’ll be fine with a basking shark. No teeth, you see. Basil, he’s called.’

‘Is this where we’ll be staying?’ Saffy asked warily, eyeing the shark jaw.

‘It is indeed,’ Isla said. She turned to the girls. ‘I’m Isla Kissick, and it’s absolutely thrilling to meet all of you. But I’m afraid I only know your mummy’s name. Why don’t you tell me your names?’

‘I’m Luna,’ Luna said. ‘I’m nine.’

‘Luna,’ Isla said. ‘What a lovely name.’