My Friend Walter by Michael Morpurgo
Bess Throckmorton meets an old man at a family reunion who tells her that Sir Walter Raleigh is one of her ancestors. Curious to see where he was imprisoned, she visits the Bloody Tower and finds that the old man was none other than Sir Walter himself! The mischievous old ghost sets about restoring the family's fortune, while all the time Bess has to try to keep the presence of a ghost in the house a secret. Sir Walter comes up with his own scheme to steal the orb from the Crown Jewels to help raise money for the farm. But the orb goes missing from hiding place and the family find they have to move out of the farm. At the last minute. Walter finds a brilliant way they can 'find' the orb and the family can finally move into the Sir Walter's old lands and to another farm they will love.