This article examines the legacy of the scandal wrought by Zola’s novel Lourdes (1894) for future controversy over the writer’s pivotal involvement in the Dreyfus Affair. Zola’s fictional account of the Pyrenean shrine—its founding apparitions, and its miracle cures— provoked a deluge of refutations from Catholic clergymen, doctors and writers. The Lourdes scandal has been understood as a flashpoint for Catholic indignation in the ongoing ‘culture wars’ of the Third Republic—one readily reignited with Zola’s intervention in the judicial handling of Dreyfus’ case. This article offers a more precise understanding of the Lourdes debates as a dress-rehearsal for the Affair that followed. It reads Catholic attacks on Zola’s naturalist novel for their shared preoccupation with proofs, expertise, authority and the status of truth and evidence, which anticipated the very terms on which his defense of the Jewish captain would be denounced. Both scandals, then, appear bound together by fundamentally literary concerns; and this article shows how quarrels over aesthetics lay at the heart of the ideological differences they described.