They came to a point where the sound of the water seemed to echo, as though it had entered a cave. The bank had risen high enough that the rocky outcroppings arched and merged together above the river. Nashua was right; the river really did go underground. Their elvan guide stepped in front of the others to prevent them from going too close to the mouth of the cave.

“Stay back,” Nashtra warned them. “It is dangerous if you get too near there.”

Cerise peered at the mouth of the case, trying to see what it was that he meant. The rock was not a typical grey. Instead, it started off as turquoise, and then faded to an ice-blue sort of crystal, which in turned darkened into a deep, rich kind of sapphire before it disappeared under the earth. The air between the arch of the cavern and the rushing water seemed to sizzle with energy, hissing in the mist of the river.

“What is going on?” Cerys asked. Her hair fell like it was standing on end, charged with some sort of electro-static energy. “Why is there so much energy right here?”

Natasha shook his head. “We do not entirely understand it,” he admitted. “What my people do know is that it is very dangerous to try to get very close to he opening of the cave.”

“Can you?” Himeko asked him.

“I should be able to, in theory, as one of the few who cab tread the river” he told her, “but I have not built up enough resistance to the river’s energy to pass safely into this cave. I wouldn’t want to anyway,” he added. “Only a few yards in, it descends into a wonderful.”

“I see,” Himeko said. “So nobody can come up into the forest through the river from the cavern.”

Nashtra nodded. “It provides a certain amount of defense, I suppose.” He glanced up at the canopy that rose up high above. “The vines you have seen hanging from the trees do a lot of the rest of the work.”

“So is there a way out of the forest from here?” Peter asked, his lack of interest in the river obvious.

“Of course,” Nashtra told them. “We just have to keep following the past of the river.”