Late in 1888, a swift and public rift occurred between Mary Baker Eddy and her student Ursula N. Gestefeld. Historians agree it was a significant break, generally glossing its cause as a personal quarrel later codified in separate organizations: Eddy's Church of Christ, Scientist, reorganized in 1892, and Gestefeld's Church of the New Thought. This article finds, however, that the rift between Eddy and Gestefeld is best explained in terms of theology and religious practice. The two expressed incompatible views of Christianity and its relationship to Theosophy, eclecticism, truth, ethics, ambiguity, and special revelation. They ultimately codified these profound religious differences, not merely personal quarrels, in their distinct churches. The article's findings cause us to rethink the scope and shape of Eddy's self-professed Christianity; the common characterization of her as excluding powerful women from her church for authoritarian reasons; and the terrain occupied by the traditions and churches Eddy and Gestefeld subsequently developed. I show that in their case, contact resulted not in combination but in conversation and contestation, and ultimately perhaps in co-existence. This builds on and sharpens the theoretics describing the religious milieu in which they operated.