Mohiam explains to Paul that the purpose of the test is to discover whether Paul is "truly human", by requiring him to endure pain and still act rationally. He passes the test, and Mohiam (though still furious over Jessica's choice to disobey the Sisterhood and bear a son instead of a daughter) is somewhat intrigued by the potential she sees in 15-year-old Paul, as she notes he has survived more pain than any other Bene Gesserit inductee. Later, Mohiam accompanies Emperor Shaddam IV to Arrakis in her role as Imperial Truthsayer; there she is faced with Paul's four-year-old sister, the pre-born Alia, whom she calls an Abomination. Mohiam is further alarmed as she witnesses the ritual battle-to-the-death between Paul and Feyd-Rautha. Paul calls Feyd "cousin," revealing that Paul is aware of the secret that the Baron Harkonnen is his grandfather. But Mohiam is most concerned with the potential outcome of the duel, which could prove to be "a major catastrophe for the Bene Gesserit breeding scheme." She realizes that "Two end products of this long and costly program faced each other in a fight to the death that might easily claim both of them. If both died here that would leave only Feyd-Rautha's bastard daughter, still a baby, an unknown, an unmeasured factor, and Alia, the Abomination." Paul is victorious; seeing the inevitability of the situation he has orchestrated, Mohiam compels Shaddam to give in to Paul's demands, allowing Paul to depose him and become Emperor in his place. In "Dune Messiah", the Reverend Mother joins the conspiracy to topple the rule of Paul Atreides after he ascends the Golden Lion Throne and unleashes his Jihad upon the Empire. She, along with the Tleilaxu Face Dancer Scytale, the Spacing Guild Navigator Edric, and Paul's embittered consort (and Shaddam's daughter) Princess Irulan of House Corrino, plot to insinuate the Tleilaxu ghola Hayt into the court to weaken Paul's confidence in his prescience and thereby ruin him. Forbidden to ever return to Arrakis, Mohiam is taken into Paul's custody when it becomes known that she is on a heighliner in orbit above the planet. Aware of the Bene Gesserit desire to acquire his genetic material for their breeding program, Paul seeks to negotiate with Mohiam.