Then, just when her face was almost on the floor, she realised there was room to stand up, so she did. She was in a green, dim space in the wood.

In front of her was a hollow tree.

It had been an oak once, enormous and ancient. Maybe lightning had blasted it, long ago, because now the inside was just a ridged and knotted emptiness.

Seren walked all around the tree. She looked up.

She had to put her head so far back it made her giddy, but there was a knotted mesh of branches up there, and high in the branches, so high it was scary, there was a nest. It was made of odd shiny things, as far as she could see. She realised what she had to do. The Egg must be in that nest, and she had to climb up and get it.

For a moment, as she hesitated, she almost thought she heard voices calling her name urgently, very faint and far away. It might have been Tomos, or the Crow. Perhaps they were looking for her. If they found her they would tell her to stop, so she slipped inside the hollow trunk of the oak, put her hands up and her foot on the twisty roots and began to climb.

It was not too difficult, rather more as if the tree had a winding staircase inside it. There were ridges of old timber, and gnarls and knots and branches to catch hold of and pull herself higher. Soon swallows and swifts circled round her. She climbed carefully past a nest of bees that buzzed in her face, through a tangle of ivy that caught in her hair. Slants of sunlight dazzled her eyes. A squirrel watched her and a hawk flew away with a flap of wings.

Soon she was breathless and her heart was thumping, but she went on, and up. Now the stairway was very tight and it was made of smaller branches that bent under her weight as if she was coming to the top. Then her head came out through a crown of leaves, and she could see for miles.

She held on tight, and stared. What a strange country it was!

Not Wales at all. Not anywhere she knew.

Great mountains surrounded it, all glassy and snow-covered. Vast unbroken forests stretched forever. And over there she could see the sea! A green, shifting ocean far in the distance, but how could that be?

Plas-y-Fran was nowhere to be seen.

This was a different world altogether.

‘Gosh,’ she said, clutching as the branches swayed.

It was too strange to think about, really, so she shifted her weight and took a breath of the cold fresh air. Then she struggled around with her back to the tree trunk, and saw the nest.

It was made of gold. She knew that at once, because it shone so brightly. It was out on a thick branch, a good way out from the main trunk. Suddenly she realised what a long way down the ground was.