Merry’s parents and Gawain arrived home in a sudden cloudburst bearing newspaper-clad bundles of take-away fish and chips.

‘Oooh, delicious!’ exclaimed Merry. ‘I’m starving.’

‘Good!’ declared her mother. ‘You’ve got your rosy cheeks and your appetite back. Good to see.’

That’d be the exercise, thought Merry.

Caradoc scooped the post off the doormat, opened it on the way to the table.

‘Yes!’ he roared, making them all jump.

He brandished a piece of paper in the air. ‘Cheque for seven thousand pounds, made out by the National Museum of Wales!’ He pulled Merry into a familiar bear hug.

Merry smiled. ‘It’s a start.’

‘With what you’ve set in motion it’ll be a finish too,’ her father added. ‘We’ll pay off our mortgage by the end of the year!’

‘If it goes according to plan,’ replied Elinor. She managed a small smile, but Merry could see her mother still lived in fear of losing their home and all that went with it. And was still judging what she saw as Merry’s rashness.

‘I wonder how Professor Parks is getting on?’ said Merry, with a frown.

‘Well, you know he came round, asking after you. Which was nice,’ added Elinor, ‘but he hadn’t found anything.’

Merry didn’t say she’d heard him come visiting, didn’t want her parents to know she’d also heard her father on the phone, heard them arguing with the bank about how they were going to pay that month’s mortgage and the arrears.

‘I might just go and take a look at the dig after lunch,’ said Merry.

‘Be a bit careful, cariad,’ cautioned her father.

She didn’t think to ask what he meant.

It had stopped raining but drops continued to plop from the branches on to the forest floor.

The fallen tree still lay prone. Merry could see no sign of Professor Parks. She crept up behind the tree and peered over the huge trunk.

The burial mound was covered in a lattice of crisscrossing fine ropes, with labelled sticks protruding from each square. It all looked very professional. And clinical. Merry felt a lurch. The chieftain would hate this.

‘I wasn’t expecting visitors,’ said a voice.

Merry let out a yell and wheeled around. Professor Parks stood behind her. Just four feet away.

‘You startled me!’ she said.

‘You shouldn’t go creeping around, then, should you,’ he replied evenly.

‘It was you who crept up on me.’ She frowned. ‘How’d you do that?’

‘You walk on the outside of your feet, rolling forward slowly.’

‘Really? And why would you know that?’

Parks laughed. ‘I stalk deer in the Scottish Highlands. Stealth is everything.’

Merry filed that away for later. ‘Found anything yet?’

‘Digs are slow and painstaking and made more so by spectators. Look, I’m sorry,’ said Parks, sounding anything but. ‘I thought I’d made it clear. We cannot afford to have the site contaminated. Again. With respect, Merry.’

‘Contaminated? You make it sound like a crime scene.’

‘It’s not dissimilar. I’m searching for evidence in a forensic manner.’

‘And there’s a dead body. We know that much.’

‘We assume that much,’ corrected Parks.

‘It’s a burial mound!’

‘But there could be more than one dead body, Merry. Ever think of that?’

Merry shuddered. One dead chieftain was bad enough.

‘I’ll leave you to it,’ she replied, turning and walking away.

She headed home through the dripping forest. She walked normally, and then she tried Parks’s trick, rolling forward on the outside of her feet. It took a while to get right, but it worked! A useful skill, she thought. If you were a hunter.

Merry’s Easter holidays had officially begun, so she had lots of free time. Every day, she’d tell her parents she was off for a run and head over to the Black Castle. They were used to her going off on hill runs for hours so it didn’t strike them as odd and they didn’t question her. Part of her felt bad at the deceit, but a stronger part of her had become obsessed by her plan.

Thanks to the SEAL’s tips, at the end of a week, she was able do fifty yards without a breath; the same distance the SEALs had to do as part of their selection. But in the de Courcys’ pool there was no current to fight. And that bothered her. She wanted to swim with more weight. She needed something like a fully weighted jacket. But what?

She found it as she checked in with Mrs Baskerville the next day.

‘They’re back tomorrow,’ said Mrs Baskerville. ‘So make the most of it.’

Merry nodded. ‘I will, thanks.’ She paused, ploughed on before she could change her mind. ‘Heard anything from James?’

For the last few days, she hadn’t texted him. Or called. For his sake, she couldn’t keep asking him what was happening with Manchester United, if they’d made him an offer. Or not. When he had good news, he’d let her know. She just had to wait and believe.

‘He texts me every so often to tell me he’s fine,’ the housekeeper said. ‘Hasn’t come home once.’ Her eyes misted over. ‘Don’t think he will neither.’

Merry gave a sad smile. ‘He’s following his dreams. That has to be a good thing.’

Mrs Baskerville turned on her with a hard look. ‘That’s what you think at sixteen. Let me tell you, not at sixty.’

‘But he is sixteen, or almost!’ protested Merry.

‘And is that what you were doing too, chasing your dreams when you got hypothermia out on the mountains?’ demanded Mrs Baskerville, hands on hips.

Merry bit her lip, didn’t answer.

‘Yes. Thought so, though God knows what you were dreaming of out there! There’s a price to chasing your dreams. And you nearly paid it in full, from what I hear,’ she added, more softly now.

‘But I didn’t,’ replied Merry just as softly. ‘I’m here now.’

‘Hmm. I don’t like any of it,’ said the housekeeper. ‘Off you go then, and do whatever it is you’re doing, you with your secrets . . .’

As she bustled away, indignant and worried, Merry’s eye turned to Sir Lancelot in the Great Hall. To his chain mail. Mrs Baskerville’s fears had rattled her. She felt she needed to train harder, to prepare better. Sir Lancelot had the answer.

Quietly, she slid the chain mail off his wooden body and pulled it on herself. It was finely wrought and loose, allowing her to move, but it was heavy. Merry reckoned it weighed a good twenty-five pounds. She clunked out of the Black Castle, along the stone path.

Inside the pool, she removed it, changed into her swimming costume, pulled her shirt back on, then slid the chain mail over it. The cotton would stop the metal cutting into her skin. She eased into the pool. The chain mail dragged her down in the water, just as she wanted. She felt a brief flutter of panic, then reminded herself she could climb out at any time, that she was fine, that she could do this.

She counted out the lengths. She managed ten, then, blowing hard, heart pounding, she took a break. After a few minutes, she started her underwater training. It was tough but she pushed on. Tired, she resolved to do another few lengths underwater when something made her pause: a disturbance in the air.

She surfaced and looked up into the astonished and furious face of the Countess de Courcy.

Merry climbed out of the pool, clinking and dripping, her blonde hair hanging to her waist. She removed her goggles. Her eye patch wasn’t in reach and she saw the countess flinch at the scarred-over empty socket of her left eye. Anne de Courcy briefly covered her mouth with her hand; then she composed herself. She planted her hands on her skinny hips, and almost spat out her words.

‘Merry Owen! What the hell do you think you are doing?’

Merry’s first thought was, What the hell are you doing back home?

She paused, stood straight. She needed to get her breath back, but she refused to let the countess think she was nervous, or intimidated in any way. She held her head high.

‘Swim training,’ she answered.

‘In my pool?’ The countess paused theatrically. ‘In my chain mail? Does Mrs Baskerville know about this?’

‘Course not.’

‘Oh, I suppose James gave you the code, did he?’

‘No, he did not. The door wasn’t closed properly. I just had to push it open.’ The lie came easily. The last thing she wanted was to get James or Mrs B in trouble.

She slipped out of the chain mail, let it clink to the ground.

‘After having helped yourself to my chain mail. Mrs Baskerville forgot what day we were coming back on. It would seem she is forgetting her duties altogether.’

The countess reached out one manicured finger and poked Merry in the chest. ‘You know you were a fool not to sell that book to me . . . silly girl that you are.’

Merry’s heart began to pound, but she kept her face impassive.

‘I’d have written you a cheque for sixty thousand there and then,’ continued the countess in her oh-so-carefully-cultivated upper-class accent. ‘That kind of money’s not easy for pony breeders to come up with, is it?’

Merry’s fury rose up in her. She struggled to keep it under control. Anne de Courcy’s eyes were sneering; she was enjoying this, enjoying the power her money gave her and the pain it could cause.

But Merry was taller than the countess, and much, much stronger.

‘Over my dead body,’ she said.

The countess laughed. ‘You’re lucky the wolfhounds didn’t catch you trespassing or else there’d be more than a dead stallion in the Owen family.’

Merry felt as if she were watching herself. Her control snapped. She reached out, grabbed the countess and pushed her hard.

Into the pool.

The countess went in with a shriek, came up spluttering and cursing.

‘Get out, Merry Owen! And stay away from James!’ she screamed, her Welsh accent resurfacing at the same time. ‘You’re damaged goods, you are. I don’t want you consorting with our family! You’re nothing but a bad influence on him!’

Merry grabbed her clothes and ran home, the sound of the countess’s scream and the echoes of her parting words playing over in her mind. There’d be a cost to what she’d done, but she didn’t care.

Even so, she struggled to sleep that night. She thought only of the black water, the evil cold of the cave behind the waterfall.

It was time to go back in.