Under their feet, the ground seemed to tremble.

Polly O'Keefe has recently moved in with her grandparents, the famous scientists Alex and Kate Murry, when she wanders into a time 3,000 years before her own. Perhaps it's not an accident - as she is told by two druids: When a gate between circles of time opens, it opens for a reason. When the gate closes behind Polly and her gravely ill friend Zachary, the reason becomes clear. In this desperate time, can Polly keep herself and Zachary alive until the gate reopens to bring them home?