An odd compulsion leads Mulder to search a nearby field where he finds an underground Civil War bunker concealing Ephesian and his six wives--all on the verge of committing mass suicide. One of the wives, Melissa, catches Mulder's attention. She feels somehow familiar to him. Ephesian, his wives and the cultists are taken into custody. But with no evidence of abuse or illegal weapons, the FBI can hold them for only one day. Mulder and Scully are assigned to interrogate Ephesian and his wives. Preaching fire and brimstone, Ephesian admits nothing.

Melissa is a different story. Under questioning, this withdrawn and hostile girl suddenly shifts personalities into the mysterious informant Sidney, a gruff male New Yorker. But somehow Mulder knows Melissa's case is even more unusual than Multiple Personality Disorder. He is certain that "Sidney" is one of Melissa's past lives. Scully, who has a hard enough time with MPD let alone reincarnation, can't understand why Mulder is so obsessed with Melissa, and so certain he is right.

Then comes a revelation that surprises even Mulder. Melissa shifts into yet another identity: a Civil War nurse named Sarah Kavanaugh. She tells them she watched as her fiancee Sullivan Biddle died in the aftermath of the long-ago battle. And that Biddle is one of Mulder's past lives. Mulder unconditionally believes her. Desperate to discover the truth...Mulder has himself regressed.

Scully listens as Mulder cycles through a series of his past lives. He says that same souls reincarnate together over and over again: he, Samantha, Scully, even the Cigarette-Smoking Man are destined to play out many lifetimes together. Melissa and Mulder are soulmates...fated always to be star-crossed lovers.

The current Melissa hears Mulder's story, but she won't allow herself to believe. She returns to Ephesian. Scully doesn't know what to think--especially when she discovers photographs of Sarah and Sullivan in historical archives.