Ziggy, Rico, Rashawn, and Jerome discover their hometown used to be a stop on the Underground Railroad and set out to explore the part of the tunnel right under their school. When a trapdoor slams behind them, locking them in the tunnel, there's only one thing they can do--plunge deeper and deeper into the darkness. Where will the tunnel lead them? And will the old, crumbling walls hold until they find their way to the end?