A suicide pact. A new responsibility. A desperate bid for harmony.

As Rainbow leaves Brocéliande forest after the events of Tree Slayer, she learns that a much greater challenge faces her. Exasperated by mankind's disrespect for trees, the One Tree has set a terrible event into motion. Rainbow is strictly forbidden from intervening, but all the trees in France could die unless she does so.

Her search for guidance will take her to England, where a startling discovery makes sense of her gift and opens new perspectives. She must take the hardest decision of her life. But will her and Eole's sacrifices be enough to save the French forests?