When construction workers find human remains in a 1950s fallout shelter, the skeleton is brought to the Jeffersonian for identification. As Zack cuts into the bone, deadly spores are released leading to the quarantine of the lab over Christmas. While everyone else tries to keep the holiday spirit up, Brennan focuses solely on solving the mystery of the man in the fallout shelter. As she works to bring closure to the unidentified man's family, being quarantined in the lab acts as a catalyst in bringing the entire team closer together.