The story takes place in contemporary England on the grounds of stately Castlemaine, part of which dates back to the twelfth century. The summer holidays are beginning, and because her bicycle is broken Heather cannot get to the village five miles away to see her friend Janine.

Heather likes to escape when the crowds of tourists arrive daily around eleven-thirty, but on this day she mistakes the time. The tourists are already blocking her path to the private castle tower.

Heather seeks a hiding-place at an isolated mound on the edge of the castle grounds, which her father believes is the site of an old ice-house. Janine, however, says that it is the burial place of Wild Robert who did witchcraft in olden days, and of his treasure. When Heather reaches the mound and finds it too dark for reading, she cries out in frustration to "Wild Robert...