A documentary filmmaker's remains are found at the bottom of an air shaft beneath the tunnels of DC with Booth and Brennan's investigation exploring a "shadow society" of possible candidates living there. These "mole people" have a social worker named Helen who cares about them and was against Marni's "exploitation" of them with a documentary on their living conditions. A traumatized soldier sensitive to light named Harold could have the answer as to who killed her, Booth and Brennan discovering bloody clothes and further bone fragments belonging to Marni. During their investigation the Jeffersonian team find that Harold has in his possession a priceless artifact which means underneath somewhere in the tunnels is a vault containing Civil War treasure..enough treasure worth killing for perhaps? After the skull is reconstructed, it is established that Marni was hit in the head with something with a V-shape point. Raw footage reveals to Bones and Booth that Marni knew of the treasure..and she wasn't the only one. Also unveiled is that Marni knew mountain climbers who taught her how to move down shafts to travel deep within the tunnels, one of two her lover. What I thought was really cool about this one was the labyrinthine maze of tunnels underneath the city and how the Jeffersonian team are able to find where the Civil War vault is. The episode starts out trying to find a killer and the result is the unearthing of a vault which has been buried away for ages. Not to mention, there's another skeleton found near where the vault is located, the dead person seemingly himself murdered by another for the treasure that the killer never found. Excellent performance from Glenn Plummer as the damaged Harold who is certain to gain sympathy from viewers as he does Bones who scolds Booth for not understanding his social standing/status among the Mole People Population.