The Rinaldi Ring by Jenny Nimmo
Sent away to live with his cousins, the Pipers, after running away from his father for the third time, Eliot is having trouble coping with the death of his mother. But at the Pipers' he is haunted by a presence from the past, a strong ghost that tears up his room, throws books at his cousins, and brings with it a strangely strong smell of flowers. Gradually, Eliot uncovers a strange story from the war, about Mary-Ellen, imprisoned in his room and ultimately threw herself off a bridge, supposedly to be mad at the death of her lover, Orlando Rinaldi, in the trenches. The sinister Freya Greymark stalks the village, holding the Rinaldi Ring, inherited from Orlando's brother, Olive, but rightfully Mary-Ellen's. The haunting gets more intense until the Pipers call Eliot's father to take him away. Running from the car, Eliot at last finds someone who can tell him the real story. The brother who died at the front was Oliver, not Orlando, but Mary-Ellen found Orlando in hospital, wounded beyond recognition, and he died before she could save him. Their baby survived, and was Eliot's grandfather. Opening up the story from the war finally allows Eliot and his father to talk about the death of his mother, and they, and their ancestors, can now rest at peace.