 Trepkos and O'Neil are officially unaccounted for and presumed dead; Trepkos is last seen carrying O'Neil's body as he disappears into the volcano.Howard Gordon was inspired to write the episode after seeing two news reports about Project Dante, a robotic explorer created by NASA that had been sent into a volcano.Chris Carter said of the episode, "I think that's the first time in our second season that we were telling what's one of our serial stories rather than our mythological stories.