Advent

the long version

"For centuries it has been locked away. Lost beneath the sea. Warded from earth, air, water, fire, spirits, thought and sight. But now magic is rising to the world once more. And a boy called Gavin, who thinks only that he is a city kid with parents who hate him, and knows only that he sees things no one else will believe, is boarding a train, alone, to Cornwall. No one will be there to meet him."--Publisher description.