15th-19th August, 1658: Luka and Emilia must travel to the New Forest to find the Wood tribe, whose charm is a rue flower, the herb of grace. Its power is that of plants and herbs which can both heal and poison. On the way, the two children tangle with an impoverished widow, the thief-taker Coldham, a highwayman and a witch, and find themselves caught up in a Royalist plot to restore King Charles II to his throne.
