This seventh and concluding volume in the Keys to the Kingdom series has two tasks: To wrap up the action of the first 6 books, and to depict adolescent struggles with identity and responsibility. As to the former, there is plenty of swashbuckling, giant pointy bugs, explosions, and the like. The plot points are resolved, though some characters and their motives remain a mystery. Why, for example, have none of the Trustees done more than allude to what they fear will happen when the Will of the Architect is re-assembled?The thematic business is captured by Arthur's shift from a human boy to an otherworldly Denizen as he uses his power. Who is Arthur, and who is Lord Arthur? This question, which has recurred throughout the series, is answered in Lord Sunday. As the mortal children Arthur and Leaf take on more burdens and responsibilities, they are both nostalgic for the sense of safety they experienced before these events, and willing, though not always glad, to take on adult roles. I was pleased that this included real choices and sacrifices, both developmental and interpersonal.