Construction workers find a skeleton in an old fallout shelter from the 1950s and the Jeffersonian is brought in to help identify the remains. When Zack cuts into the bone, he accidentally releases spores of the deadly fungus Valley Fever, causing the team to be quarantined in the lab over Christmas. While everyone tries to maintain the holiday spirit, Brennan buckles down to solve the mystery of the fallout shelter. Booth and Brennan's team are reminded that this is a rough time of year for Brennan, since her parents went missing right before Christmas when she was a kid. As Brennan works to bring closure to the family of the missing man - something she has yet to receive about her own parents - the time spent together in the lab provides the catalyst for revealing information about all of them.