Moya thinks she hears a distress call from another pregnant Leviathan and goes tearing off into space to lend her assistance. When they get there, however, they find that "there" is the New Moon of Delvia, and it wasn't a Leviathan calling but a high level Pa'u named Tahleen. She and her father, Tuzak, are the leaders of a breakaway sect of Delvians who want to overthrow the corrupt regime on their home planet. Unfortunately, they tried to proceed too quickly and are descending into insanity, a consequence that Delvians suffer when they give in to their dark impulses. And for a bunch of holy people, they certainly seem to have a lot of dark impulses.
Tahleen needs Zhaan to show her the path to serenity via a Delvian ritual called unity. Before she agrees to take part in this ceremony, Zhaan goes to John for advice. She has Tahleen telepathically show him the crime she had been imprisoned for, the murder Bitaal, her lover and the leader who sold Delvia out to the Peacekeepers. Zhaan goes ahead with the unity despite John's advice against it, but Tahleen is greedy. She doesn't want to be shown the path to serenity, she wants to steal it from Zhaan. As soon as she realizes Tahleen's intent, Zhaan breaks the unity but it may be too late. She's already slipping toward insanity.
To keep them from interfering with her machinations, Tahleen urges her followers to cloud the minds of Moya's crew. Aeryn thinks she's lost her ability to function as a soldier, Rygel believes he's shrinking, and D'Argo sees his son being pursued by a Peacekeeper. Lorana, one of the Delvians, makes John think she's Alex, the sweetheart who dumped him in favor of a study grant. In this form she tries (unsuccessfully) to keep his mind away from Zhaan's troubles.
Tahleen kills her father to keep him from influencing the other Delvians and the next time we see Zhaan, she's using Tuzak's dead body for a pillow and plotting Tahleen's murder.
Lorana releases John from his hallucination and tells him that if he shares unity with Zhaan, he may be able to help her overcome the creeping insanity. During the unity, John is able to show Zhaan the part of him that sees her as a gentle giving being and focusing on this saves her from madness. Because she now feels unworthy of being a Pa'u, she gives up her vestments but tells John the she will someday become one again.