This third volume of The Dark is Rising sequence returns us to the Drew children and the theft of the Trewissick Grail they found at the end at the first book, Over Sea, Under Stone. How the priceless artifact was stolen from a museum baffles the police, as there is no evidence of a break-in. Merry confirms what the children suspect: the Dark took it. He asks them to come with him back to Cornwall during the Easter break.
As it happens, Will Stanton from the second book, The Dark is Rising, is also headed there with his Uncle Bill. None other than Merry picks them up at Will's house, but neither give away the fact they already know each other. The Drew boys do not like Will, for how are they going to find the grail again if some other boy is always going to be with them?
The boys' sister, Jane, accepts the nocturnal invitation to attend the annual, ladies-only, making of the Greenwitch, a tall figure made of leaves and branches, who the women then ask for whatever they wish. Only Jane feels the tremendous power in the figure - and its terrible loneliness. Her wish is for it to be happy. The leader of the event tells her this is a dangerous thing to request. The event ends in the morning with the figure cast off a cliff into the sea.
Will and Merry discuss the latest disguise a member of the Dark has taken: a painter who stole a picture Barney made and who also tried to break into the crowd around the Greenwitch just before it tumbled into the water. Simon and Barney follow Rufus the dog to the painter's home. Barney finds not only his painting but the stolen grail.
Will and Merry launch a desperate search for the Greenwitch and what it possesses: the lost manuscript from the first book that would give the Dark terrible power if used in conjunction with the grail.
Will and Merry are not the only one who seek the Greenwitch. What is that painter doing out after dark? And what does Jane's wish for the witch's happiness have to do with it?
I didn't like this book as much as the first two because it was not as interesting or exciting until towards the end.