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?