Journeys Of The Guardians' Key

One day a boy called David finds a strange object, a segment from a sphere fashioned from an unidentifiable material, in a tree in his garden. David puzzles over the segment and the mystery soon deepens when his cousin Melissa arrives from America bearing a similar piece she has found in her garden back home. They and five other people from around the world have been chosen to restore the Key, but sinister forces with agendas that would be halted by the rejoining of the Key will stop at nothing to prevent them from achieving their goal.