Tosia and Michael find strange markings on an ancient oak in the forest, and the tree opens to reveal a blue-lit portal that seems to be calling them forward.
Tosia was late again. She sprinted across the yard, skirting the neighbour's beige cat, until she reached the gate where Michael was waiting, one hand on his bike and the other on his hip.
"At last," he said, pretending to sound annoyed. His grin gave him away.
Tosia stuck out her tongue and hoisted her rucksack higher. A torch handle and the corner of a notepad poked out from the top.
"Come on," she said. "If we don't get there before the rain starts, we'll miss the Old Oak."
They set off at once, cutting across fields and meadows already turning gold under the August sun. Ahead of them, the forest waited at the edge of the village, dark and cool and full of whispers. That was why they liked it. Nothing there ever stayed ordinary for long.
The Old Oak stood just inside the trees, enormous and bent with age, its trunk split by a hollow so wide Michael could have hidden inside it completely.
"I heard a fox lives in there," Tosia said, lowering her voice as they came closer.
Michael snorted and took a compass from his pocket. It had belonged to his grandfather, and he liked to spin it open as if it could point to more than north.
"A fox?" he said. "More like a dwarf."
When they reached the tree, the wind shifted. The leaves shivered overhead, and the sky seemed to press lower between the branches. Tosia crouched beside the trunk and saw it first: strange grooves cut into the bark, curling spirals and sharp little arrows, as if someone had tried to draw a map into the wood.
"Michael," she whispered, "look at this."
He stepped beside her and touched one of the marks with his fingertips.
The oak shuddered.
Its roots jerked beneath the soil. The bark split with a deep, cracking sound, and a circle of blue light opened in the trunk where there had been only dark wood a moment before. It was the shape of a door, but it did not lead to the hollow. It led somewhere else.
Tosia forgot to breathe.
A soft whisper drifted out of the opening, so faint she could not tell whether it was a voice or the wind speaking through a distant place. The blue light pulsed once, twice, and the whole tree hummed low and steady, like a note held too long.
Michael looked at Tosia. Even in the dim light, she could see the excitement in his face, and the fear hiding just behind it.
"Do you hear that?" he murmured.
Tosia nodded.
The whisper came again, clearer this time, as if someone on the other side had noticed them at last.
"Are we going in?" she asked.
The light flared brighter, and from deep inside the tree came a sound like footsteps moving closer.