Shade's Children by Garth Nix

In a dystopian future where all adults have vanished, children are harvested by sinister Overlords for their organs and body parts. A group of teenagers, guided by a mysterious artificial intelligence named Shade, struggle to survive and resist their grim fate. As they navigate a world filled with monstrous creatures and deadly challenges, they uncover secrets about their past and the true nature of their existence, leading to a daring plan to overthrow their oppressors and reclaim their future.

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