The remains of a young documentary filmmaker are found in a ventilation shaft in an underground Washington, DC, tunnel. The investigation leads the team to a society living in the tunnels and a lost treasure of American art. 

The team gets a case of pirate fever when a dead body is found clutching a 300-year-old finger bone. Not only does the team need to solve the murder, but they may also prove the existence of a long sought after pirate treasure.