S4, E21: When a real human skeleton is found being used as a stage prop for a death metal band in Norway, authorities determine the victim was an American citizen. The Jeffersonian team tracks the skeletal remains to an underground U.S. death metal band and identifies the victim as a bassist named Mayhem from a band called Spew. As Booth and Brennan venture into the unfamiliar world of death metal music to search for the killer and a motive, they learn about their own team's surprising musical preferences and gain new insight into Sweets' past. Meanwhile, when Sweets asks Dr. Gordon Wyatt (guest star Stephen Fry) for input on the book he's writing about Booth and Brennan, Dr. Wyatt lends Sweets an interesting perspective on the pair's unique relationship.