The French mystic Jean-Joseph Surin (1600–65) was the chief exorcist during the infamous demonic possession in Loudun in 1634–37. During the exorcism, a demon entered Surin’s own soul, and the exorcist became demoniac. He spent the following eighteen years of his life mute and paralyzed. All the while his troubled mind conversed with God, and he composed hymns and poems that tried to comprehend his agony. Surin left detailed descriptions of the dramatic events that shaped his life and fascinated his fellow Jesuits. But Surin was also an author of spiritual texts, a spiritual director of...