Grail
From The Dark is Rising Wikia
The Holy Grail, also known as the sangraal, was one of the Things of Power, and was the key, and had a prophecy.
It is found by the Drew children in a cave in Over Sea, Under Stone.
The grail is stored in the British museum and labeled "Trewissick Grail", it is valued at 50,000 pounds, though the curator said it was "priceless". It is listed as a 6th century celtic chalice made of gold.
In Greenwitch, the grail is stolen from the British museum by the Dark, and the search for the parchment in the lead case that was with the Grail commences. The Light and the Dark try to gain the secret from the Greenwitch, who has claimed it as his treasure. Jane Drew is finally given the secret, and the Grail is found in the Dark gypsy's home.
The Grail and the parchment within the case give the Light the second prophetic poem.
