'A Fake Saint and the True Church' offers the remarkable story of a fake saint to contemplate the meaning of truth. It follows the efforts made by the supposed saint's (real) 17th-century descendant to promote his cult in Naples and Rome. This story reminds us that distinguishing the true from the false is a matter of commitment and belief, not simply research ability. Compared with our early modern predecessors, we are more skilled at verifying facts and less willing to let supernatural truths regulate our behaviours. Yet, the relationship between truth and authenticity is still a challenge for us, as it was for them.