‘What happened?’

Seth’s expression had been stripped back to panic, his face a shade of pale that made everything else about him look darker. ‘After dinner, he asked my mother why she didn’t like you and she said it was because you were only pretending to look after him, and he told her she should be happy because you saved him from drowning and he could have been dead.’

Tears started racing down my face. Dear, sweet Jack.

‘Mum lost the plot, said she couldn’t believe I’d allowed him to go near the sea on his own, that I wasn’t a fit father and it proved she was right to take Jack away from here.’ The pain in his eyes was almost too much to bear. ‘Jack overheard, said he didn’t want to go. She said he didn’t have a choice and told him to go to his room.’

I managed to choke out, ‘But he didn’t?’

Seth nodded. ‘He did. I went straight up to talk to him, but he wouldn’t respond, so I sent Digby up to keep him company and came back to talk to my mother. We just ended up rowing as usual, and when I went back up he wasn’t there.’

‘Where’s Digby?’ I looked around, half expecting to see the dog on the rug in front of the blazing fireplace.

‘He’s gone too.’

I swiped my hand across my nose. ‘That’s good,’ I said. ‘That he’s gone with Jack.’

‘How, exactly?’ I spun round to see Felicity standing by the window, looking older than the last time I’d seen her. Her eyes were cavernous and her hair had dropped, as though it didn’t have the heart to stay up. ‘This isn’t an episode of Lassie,’ she said. ‘The dog’s not going to run in and bark a few times, and lead us to my grandson.’

‘OK, well, have you double-checked every room?’ I looked back at Seth. ‘It sounds silly, but my friend and her boyfriend once lost his little sister, but she’d been hiding in her bed all along and had fallen asleep.’

‘For heaven’s sake.’ Felicity’s expression stretched with disbelief. ‘We’re not imbeciles.’

‘Mum, stop it.’ Seth was pacing the kitchen in his coat, his hair pushed into peaks, a powerful looking torch dangling in one hand. ‘We’ve double-checked inside and out.’ I spotted a rim of sandy mud circling the toes of his and Felicity’s boots. ‘He’s taken his coat and wellingtons, his rucksack, and Digby’s lead.’

I met his eye, and knew he was thinking the same thing. If Digby was on his lead, there was less chance of him running into the sea.

‘I thought he might have found his way to your house, there’s a bus service, I checked, because he couldn’t walk that far…’

‘Would he have any money on him?’

Seth pushed a hand through his hair again. ‘I don’t think so, he has a savings account, but no cash.’

‘It’s gone nine o’clock,’ I said. ‘It’s time to call the police.’

‘Oh god, do we have to?’ Felicity’s voice rose with fright, and I sensed it was because the arrival of uniformed officers would make Jack’s disappearance real.

‘Yes, we do.’ A strange calmness settled over me. ‘It’s dark and it’s late. We need all the help we can get.’

Seth motioned to the handset on the worktop. ‘I was about to, but hoped you might have spotted him on the way over.’

‘Oh my god, he could be lying dead in a ditch,’ Felicity wailed.

‘Not helpful.’ I fixed my eyes on Seth’s. ‘You’ve searched the beach?’

‘First place I looked, after…’ He eyed his mother who was reeling around with her hands clamped to her mouth. ‘After last time.’ He looked as if he might be sick at the realisation that, once again, his son had left the cottage without his knowledge. ‘There were no footsteps or paw prints that I could see, but I’m going to look again.’ He was already heading to the door. ‘Call the police, the lifeguard… everyone,’ he ordered his mother.

She pressed a shaking hand to her throat as he left. ‘You saved my grandson’s life,’ she said, as if that part had just sunk in. ‘Please help find him, Tilly.’ She held out a wavering hand. ‘I can’t bear that this has happened because of what I said.’

I snatched up the handset and thrust it at her. ‘Call for help, now,’ I instructed. ‘Stay here, in case Jack comes back.’

Outside, the wind cut through my denim jacket – the first thing I’d picked up after telling Seth I was on my way, leaving Bridget with instructions to call me if Jack should, by some miracle, turn up at the house.

The moon was high in the sky, lighting a path to the beach as I ran after Seth. ‘I don’t even know where to look,’ he said as I caught up. He spun back and forth, swinging the torch to and fro. The tide was creeping in, the surface rippled by the wind, waves frothing at the sand. ‘There’s no one around, so we can’t even ask if anyone saw him.’

‘I think he’d stick close to the headland, after what happened before,’ I said. ‘Let’s try over there, and see if we can pick up a trail.’

I could hear the sound of our breathing and the echo of my heartbeat in my ears.

‘Tilly, look!’ I ran over to where Seth was shining the torch. ‘Do these look like paw prints to you?’

I peered to where the beam was pointing. ‘Definitely.’ As I looked around, Jack’s voice zoomed into my head. Dad, can we go to the smugglers’ cave on the beach?

‘I think I know where he might have gone,’ I said.

Seth shone the torch at my face. ‘Where?’

Shielding my eyes, I said, ‘The smugglers’ caves I told you about, when he asked if you could take him there.’

‘You think?’ The hope in his voice was hard to hear.

‘He said he had a map on his iPad,’ I said. ‘Do you know if he took it with him?’

He smacked a fist to his forehead. ‘I didn’t think to look.’ He groaned. ‘Mum’s right. I’m the worst bloody dad ever.’

‘No you’re not.’ I punched his arm. ‘Come on. I know where they are.’ I didn’t add that we needed to hurry as the incoming tide would flood the caves within half an hour, but Seth was already charging ahead, torchlight bouncing. I also didn’t add that he didn’t need it, the moon was bright enough, because I knew he needed to feel he was doing something useful.

‘I should have just taken him that day,’ he said as I caught up. ‘I know I can’t keep him wrapped in cotton wool, but then he does something like this and I want to keep him locked inside forever.’

‘It’s a balancing act,’ I panted, as though I’d had experience. ‘Hardly anyone gets it right all the time.’

‘Are we far away?’

‘Another few minutes.’ I picked up speed so I was almost running, wishing I’d pushed my feet into my boots instead of the sheepskin slippers nearest to the front door. It was a measure of how serious the situation was that no one – least of all me – had noticed until now.

‘It’ll be freezing in those caves.’ Seth was keeping pace, his coat flapping around his knees. It was his purple-lined pea coat, and I thought how incongruous we would look to anyone watching.

‘At least he dressed sensibly.’ Even so, I knew the temperature would be arctic. Those caves were chilly even in summer. I’d explored them once with Dad, ages before I met Cassie and Meg. I’d thought it would be exciting, like in the Enid Blyton books I’d read, but had found them claustrophobic and scary.

‘I’m not going to let Mum take him.’ Seth’s voice had hardened. ‘The set-up we’ve got isn’t perfect, but it’ll get better.’

‘Of course it will.’

‘If anything’s happened to him…’

I caught the sheen of tears in his eyes. ‘Don’t think like that.’ I reached over and touched his hand and he caught my fingers.

‘Thanks for coming.’

‘Let’s just get there.’ A sudden choke of fear rushed up my throat. ‘We can’t be far away now.’

‘Jack!’ Seth called, his voice snatched by the wind.

‘Digby!’ I was rewarded by a distant bark. ‘Did you hear that?’

Seth was already stumbling ahead and, rounding a curve, I realised we were there. The mouths of the caves gaped like missing teeth and behind us the sea lapped closer. I shivered as Seth passed me the torch and cupped his mouth with his hands.

‘Digby!’

A volley of barks echoed back, followed by a wavering cry of, ‘Dad?’

‘Jack!’

‘In there.’ I pointed to the nearest cave.

Seth plunged in and I followed, shooting a hand out to the damp-slicked wall, blinking in the salty darkness. Now we needed the torch, the beam had faded.

‘Jack!’ I yelled. The sea shushed behind us. I estimated we had around fifteen minutes to get out and pressed forward, almost crashing into Seth. One of my slippers came off. I felt cold, compacted sand underfoot, but knew there were stones and rocks further inside the cave.

‘Jack!’ Seth’s shout bounced around us.

‘Dad!’ Jack’s voice broke on a sob. ‘I’ve hurt my ankle.’

‘Hang on, son, we’re nearly there.’ Seth sounded grimly determined now, pushing further into the tomb-like interior.

More barking, closer this time, and a pair of glowing eyes appeared in the weakening cone of torchlight. ‘It’s Digby.’

He lolloped over, pranced in a circle twice, then headed back the way he’d come.

‘He’s doing a Lassie.’ Hysterical laughter rose. ‘He’s leading us to Jack.’

‘I bloody hope so.’ Seth spoke through gritted teeth as he tripped over a protruding rock. ‘Jack!’ he called again.

A ghostly white light appeared. ‘What’s that?’ Seth paused in a half crouch and held up a hand, like a modern-day Indiana Jones.

‘It’s his iPad,’ I said. ‘He must have brought it with him.’

‘Dad!’

Seth clattered forward. ‘I’m here, Jack.’

I lurched behind, stifling a yelp when my foot caught the craggy edge of a rock, and as Seth dropped to hold Jack in an awkward hug, murmuring endearments, I saw that Jack’s ankle was trapped inside a narrow crevice.

‘I was climbing over, so I could get to the dry bit where it’s safe from the sea,’ he said, his eyes like big dark puddles in the bright light of his screen. ‘Digby and me were going to stay here until Grandma goes home, but I fell and my foot got stuck.’

‘Oh, Jack,’ said Seth, stroking his son’s hair. ‘You know I’m not letting you go back to live with her, don’t you?’

‘She might make you.’

‘No chance,’ said Seth. ‘I’m your dad and I love you, and you’re staying here with me.’

‘And he doesn’t mean in this cave,’ I said, relief making me silly.

‘I left a note to say where I was.’ Jack had started crying in little gulps. ‘I didn’t want you to be worried.’

‘I didn’t see it.’ Seth sounded as if he was trying not to weep too.

‘I said not to look for me until tomorrow,’ Jack said, burying his head against Seth’s shoulder. ‘I want to go to the party like Romy.’

Seth kissed his head. ‘And you will,’ he said fervently. ‘I promise you that.’

The sea had reached the mouth of the cave, sloshing gently.

‘We have to go, if we don’t want to be stuck here until the tide goes out,’ I said to Seth.

Picking up on my tone, he looked to where Jack’s foot was stuck fast, his leg twisted awkwardly. He shifted round. ‘OK, buddy, just a couple of minutes and we can go home and have something to eat.’

‘It hurts a bit.’ Jack had stopped crying, his voice wobbly but brave.

‘It’s because you’ve fallen over.’ I bent to take a closer look. ‘He’s at an angle,’ I told Seth. ‘If you can lift him up a few inches so his leg straightens, we should be able to get his foot out of his wellie.’

‘Let’s do it.’

Digby darted back and forth, barking at the water. He was skittish; sensing danger – or picking up on our tones.

‘Try and wiggle your toes,’ I said to Jack, to distract him as Seth slipped his hands under Jack’s armpits and carefully raised him off the ground, so his leg was level with the rock.

‘Ow, ow, ow,’ cried Jack, and Digby rushed to lick his face.

‘Nearly there,’ I said. I nodded at Seth who gave a gentle tug as I held onto the toe of Jack’s boot. ‘Once more.’ The icy water was lapping around my feet now. Seth gave another yank, and this time I felt Jack’s foot move. ‘Again.’

It was heart-wrenching hearing Jack sob, and I sensed Seth’s hesitation. ‘Now,’ I said. He pulled again and Jack screamed as his foot was wrenched from his boot. Digby whined and growled.

‘It’s OK,’ I said. ‘We’re done.’ I grabbed Jack’s rucksack and iPad and the torch, which had finally died, while Seth waded through ankle deep water to the mouth of the cave with Jack in his arms. The moon had dipped, but there was just enough light to make out the steps carved into the hillside, which I remembered climbing years ago, and Digby led the way to the top where we carried on walking, and didn’t stop until we were back at the cottage.