Silver on the Tree by Susan CooperAladdin Paperbacks, 1986 (originally 1977)

Cooper ties everything up neatly, but in a way that’s satisfying, that isn’t too neat or totally predictable. She also nicely shifts the focus, at the end, to humanism: a world that’s determined less by fate than by choice, and somehow manages to make this ring true, despite the fact that the rest of the series has been all about Destiny Being Fulfilled.