Meet Amber, a curious and detail-obsessed 10-year-old who feels more at home with ancient artefacts than with her peers. Her solitary life takes a dramatic turn when developers threaten to demolish her family's museum, the treasure trove of Anglo-Saxon history. Just as Amber grapples with this looming disaster, her mother, an eminent archaeologist is called away, leaving her in the care of Great-Aunt Sarah, whose mysterious stories of a magical jewel ignite Amber's imagination.
During a moment of anger and desperation, Amber discovers the twisted double oak tree in the woods, a portal to a time long past. Stepping through, she finds herself in a Saxon village where her modern worries seem to melt away. Here, she meets Aedre, a brave girl dreaming of becoming a warrior; Rinc, a local bully who constantly tests her resolve; and Bearn, a charismatic steward with a hidden agenda. She also encounters the enigmatic Aemelwold, a disfigured druid with secret ties to Aunt Sarah's past.
As Amber navigates her new world, she secretly discovers the legendary jewel and uncovers a plot to overthrow King Alfred. Watching Lady Aethelflaed rule in her father's absence, Amber is inspired by her strength and leadership as a woman in a male-dominated world. Encountering difficulties, she never knew existed, Amber's spirit is recognised, leading her and Aedre to embark on shield maiden training. Facing treachery, raids, and a climactic battle with Viking invaders, Amber must find the courage to make impossible choices.