I Am Matthew, the Cooper's Son. (Closing the Ring).

When the baseball pitch on the American Airbase of Lakenheath is dug up, the grave reveals an Anglo-Saxon Knight on his horse, surrounded by children. The Knight had not followed the code of the Brotherhood and was doomed to reside in Neitherland until a Seeker, appointed and aided by Morgan le Fey, could lead him and the children out of Neitherland into the Hereafter, before the Knight's bones are taken away for all the world to see. The Seeker is Matthew, the cooper's son, from the 14th century who meets Edwin, a lonely eleven-year-old boy, the son of a former pilot from the American base. Matthew is a ghost, or, as Edwin says, an imprint of his personality. Matthew is invisible to Edwin's parents and worries them. Isn't an eleven-year-old y too old to have an imaginary friend? Edwin tries to help Matthew solve the tasks and the riddles set by Morgan le Fey when Matthew was taken to Camelot, but time is running out. Matthew's life must hold some clues, Edwin says, and so the boy from the 14th century starts his story: I am Matthew, the cooper's son.