Books like Downsiders

Talon lives Downside, that is, underneath New York City. There is a strict code of secrecy among the Downsiders. However, when Talon accidentally meets a young woman named Lindsay, who is a Topsider (from above the ground), the two worlds inevitably collide. They become friends and love blossoms. The punishment for Talon's lack of discretion could be death. What will happen to them? Will the entire Downsider community be discovered?