The Eye of Apollo by G. K. Chesterton

When a blind follower of a strange new religion falls to her death from an office building, Father Brown suspects it was no accident. The mysterious “Eye of Apollo” cult and its charismatic leader hold the key to the crime. As Brown calmly observes and questions, the truth emerges with moral clarity. The plot blends spiritual manipulation with practical deduction. A philosophical mystery where insight, not vision, solves the case.