Young Trevor McKinney, troubled by his mother's alcoholism and fears of his abusive but absent father, is caught up by an intriguing assignment from his new social studies teacher, Mr. Simonet. The assignment: think of something to change the world and put it into action. Trevor conjures the notion of paying a favor not back, but forward--repaying good deeds not with payback, but with new good deeds done to three new people. Trevor's efforts to make good on his idea bring a revolution not only in the lives of himself, his mother and his physically and emotionally scarred teacher, but in those of an ever-widening circle of people completely unknown to him.

When 13 year old Maria Merryweather's father dies, leaving her orphaned and homeless, she is forced to leave her luxurious London life to go and live with Sir Benjamin, an eccentric uncle she didn't know she had, at the mysterious Moonacre Manor. Soon Maria finds herself in a crumbling moonlit world torn apart by the hatred of an ancient feud with the dark and sinister De Noir family. Maria discovers that she is the last Moon Princess and, guided by an unlikely mix of allies, she must overcome her family's pride in order to unearth the secrets of the past before the 5000th moon rises and Moonacre disappears into the sea forever.