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. In exchange for the guaranteed safety of his concubine Chani, and the Sisterhood's acceptance of his decision to father no heirs with the Princess Irulan, Paul offers something of the utmost value: his sperm. This is a complicated proposition for Mohiam, however, because artificial insemination is forbidden in the wake of the Butlerian Jihad.
When the conspiracy ultimately fails and Scytale is killed, Edric is executed in 10,207 A.G. by Fremen Naib Stilgar, on orders from Alia. Stilgar also puts Mohiam to death, despite previous orders from Paul to spare her life.
Read more about this topic: Gaius Helen Mohiam