Alone: The Striped Souls (Alone #13)

Even as his friends seem finally on the verge of being reunited after all their adventures, the time has come for Dodzi to regain his freedom. He must first pass the test prepared by his kidnapper, the Mad Master: an obstacle course with, perhaps, at the end, his release. Except the young boy doesn't trust that deal, and plans to escape his own way. But nothing has prepared him for the extraordinary discoveries he's about to make.