A teenage boy has turned up in Snowdonia, barely conscious and babbling about beautiful women and fairy feasts. The authorities blame magic mushrooms. The wise women say different and they want dryad's son, Daniel Mackmain, to investigate. He needs to watch his step in the mountains. Those who live in the hollow hills mask their secrets and intentions with sly half-truths. Far from the woods he knows, Dan needs help from the allies...