The film inquires into an affair of state which shook the end of the sixteenth century. It shows how the devilries of Marthe Brossier, who claimed to be possessed, led her contemporaries to clarify their thinking on the relationship between religion and science, between God and state. Four historians dissect the plot staged by Catholic zealots to sabotage the reconciliation policy pursued by Henry IV. This policy, which puts an end to religious wars, heralds the birth of the modern state and the genesis of a new world where religion is separated from politics. Our world.