Greenwitch (The Dark is Rising Sequence)

Simon, Jane, and Barney, enlisted by their mysterious great-uncle, arrive in a small coastal town to recover a priceless golden grail stolen by the forces of evil -- Dark. They are not at first aware of the strange powers of another boy brought to help, Will Stanton -- nor of the sinister significance of the Greenwitch, an image of leaves and branches that for centuries has been cast into the sea for good luck in fishing and harvest.
Their search for the grail sets into motion a series of disturbing, sometimes dangerous events that, at their climax, bring forth a gift that, for a time at least, will keep the Dark from rising.

Susan Cooper is one of our foremost fantasy authors; her classic five-book fantasy sequence The Dark Is Rising has sold millions of copies worldwide. Her books’ accolades include the Newbery Medal, a Newbery Honor, the Boston Globe–Horn Book Award, and five shortlists for the Carnegie Medal. She combines fantasy with history in Victory (a Washington Post Top Ten Books for Children pick), King of Shadows, Ghost Hawk, and her magical The Boggart and the Monster, second in a trilogy, which won the Scottish Arts Council’s Children’s Book Award. Susan Cooper lives on a saltmarsh island in Massachusetts, and you can visit her online at TheLostLand.com.