Merry crossed the de Courcy land. She knew she was barred, could almost feel the Black Castle glowering down at her from its hilltop perch, and imagined the Earl de Courcy, binoculars pinned to his disapproving eyes, spying. Maybe he’d set the wolfhounds on them both.

‘He’d love that, wouldn’t he?’ she said into Jacintha’s ear, and cantered on for another few hundred yards, making her point. She could see James crossing over the moat, disappearing under the teeth of the portcullis. And his mother.

‘Better go back, girl,’ she said to Jacintha at last. ‘Don’t want you killed too.’

Safely over the wall and back on her own land, Merry hacked on towards the Black Wood. It was an ancient forest, said to be thousands of years old. She wasn’t sure if it had taken its name from the thickness of the trees, which on all but the sunniest of days seemed to turn day into night, or because of its proximity to the Black Castle. The forest spread across both the Owens’ land and the de Courcy estate. The trees respected no boundaries and there was no dividing wall within the forest itself.

Merry spotted a narrow break and entered the trees, following a natural pathway, perhaps made by deer and her own ponies seeking shelter. The sun was warm on her face and she could smell the sweet, earthy scent of her pony’s sweat.

Birdsong rang out: thrushes, robins, finches. Merry was sure she heard a nightingale, after which the valley of Nanteos was named, but the notes of its song grew fainter, as if the bird were moving away, leading them deeper into the forest. With a light squeeze of her legs, Merry guided Jacintha to follow it. Jacintha was nervous. Ponies were prey animals, and the forest was anything but silent. The trees spoke to one another in surprisingly high-pitched squeaks as wood rubbed against wood in the gentle breeze.

Pony and rider meandered off the path, on to a smaller track. Merry ducked under low-hanging branches, gazing around her. She knew almost all her family’s lands intimately, but this part she had never explored closely. Legend had it that the forest was haunted. Looking around, Merry could almost believe it. Moss climbed up the tree trunks, shrouded the branches, fell in tendrils towards the earth, velvet green, pervasive, almost prehistoric.

The nightingale fell silent. Jacintha stopped abruptly.

‘What is it?’ asked Merry, looking around. Not the wolfhounds, she prayed, fear flickering through her. She slid off Jacintha’s back, grabbed a solid branch and, heaving on it, broke it off the tree with a loud crack that echoed round the forest.

But Jacintha was still standing to attention, so Merry felt sure the wolfhounds were not there. She would have heard them by now, and Jacintha would be more frightened. So what was it? She led her pony forward, under an especially low-hanging branch.

‘Ah! So that’s it.’

Ahead of them was a huge, uprooted oak tree, its roots tilted skyward. Merry felt a pang. The oak was a healthy one, probably at least four hundred years old.

‘What have you seen, old tree?’ she asked softly. ‘Did the spring gales bring you down?’

She hooked Jacintha’s reins over a branch and went closer. The tree had fallen at a strange angle, over an oddly symmetrical mound of earth over twenty feet long and about ten feet high. It looked man-made. Like the burial mounds she’d studied in her history lessons. The tree must have grown over the top of it.

She skirted back to the roots. There was a huge, gaping hole where the roots had been. Merry paused, tilted her head. Something was down there, a rectangular shape. Intrigued, she scrambled down, muddying her hands as she slipped. Then she reached down, worked on the earth, and pulled the object free.

It was a small chest, the size of a large shoebox. She brushed off more dirt, revealing ornately worked metal. It looked very old. She felt a sudden wariness. Was this how Howard Carter and Lord Carnarvon felt when they stood on the threshold of Tutankhamen’s tomb, when they first caught the gleam of gold within? Before the supposed curse of Tutankhamen took Carnarvon’s life six weeks later?

Don’t be ridiculous, she chided herself. It’s just an old chest. In Wales.

Yes, said a competing voice, but it might be from a tomb just the same.

There was a clasp, rusty, rough-edged. Merry tried to prise it open it but it wouldn’t yield. She fiddled, pulled, pried, cut herself, swore.

Then with something between a hiss and a sigh, the chest opened. Inside was an oblong bundle covered in tatty cloth the colour of old leaves. Biting her lip, Merry unwound the cloth. It spooled at her feet like the wrappings of a mummy.

Inside was a book.

It was ancient-looking, written in an elaborate, cursive script on pale parchment. She thought it looked like old Welsh. Some pages were illustrated with beautiful and detailed coloured drawings.

‘Wow! What have we got here?’ Merry whispered, shivering slightly. Whatever it was, it must have been a treasured possession of whichever Welsh chieftain had been buried in the mound. She quickly wrapped up the book again and replaced it in the metal chest, then stood still, thinking. After a few minutes she carried it back to Jacintha. The pony snorted and tossed her head.

‘Hey, it’s all right Jac,’ murmured Merry. ‘Nothing in here to hurt you. ‘

She stroked Jacintha’s warm muscled neck, soothing her, then, unusually awkward as she clasped the chest under her arm, she stood on a branch of the fallen tree, mounted her pony and rode from the forest.

Jacintha was skittish all the way, shied at every sound. Bareback, encumbered by the chest, Merry nearly tumbled a few times.

‘Calm down, Jac,’ she crooned. ‘Everything’s fine.’

Except that it wasn’t.