Shade's Children by Garth Nix - In the brutal world of Shade's Children, your 14th birthday is your last. Malevolent Overlords rule the earth, directing hideous, humanoid creatures to harvest the brains and muscles of teens for use in engineering foul beasts to fight senseless wars. Young Gold-Eye escapes this horrific fate, fleeing the dormitories before his Sad Birthday. He is rescued from certain doom by other refugees who live in an abandoned submarine and work for Shade, a strange, computer-generated adult. Shade provides food and shelter in exchange for information that the children gather on dangerous forays into Overlord territory. But what does Shade really want? He is a sworn enemy of the Overlords, but his use of the children to gain knowledge and power seems uncaring and ruthless. Finally, Gold-Eye and his new friends set out to destroy the Overlords--with or without the enigmatic, dangerous Shade.