Simon, Jane and Barney Drew are once more on holiday in Trewissick in Cornwall with their Great-Uncle Merry. Jane is allowed to witness an old local ritual, in which the women of the village create a giant figure woven of hawthorn branches as an offering for the sea goddess. This figure – the Greenwitch – is both eerie and menacing, yet Jane also senses its melancholy loneliness. She makes a wish that it might be happy – a wish that will have a fateful effect on the battle between the Old Ones and the Dark.