The Boxes is one of Sleator's best novels.
Taking the ancient Greek myth of Pandora and her box and turning it on its head, The Boxes has many plot twists, menacing events, tense scenes, and amazing settings, and it sparkles with intelligence. In it, Annie is asked by her beloved but mysterious Uncle Marco to guard two boxes, one made of wood, the other metal. Uncle Marco forbids Annie to open either one, and tells her to never let them be together. But Annie peeks into them, the first time she has ever defied a grownup's orders. By doing so, she is taking the first step toward being an independent-minded person; she begins her journey from passivity to intelligent action.