Reinmar of Bielau, called Reynevan, flees after being caught in an affair with a knight's wife.
With strange, mystical forces gathering in the shadows and pursued not only by the Stercza brothers bent on vengeance, but also by the Holy Inquisition, Reynevan finds himself in the Narrenturm, the Tower of Fools, a medieval asylum for the mad, or for those who dare to think differently and challenge the prevailing order.
The 'patients' of this institution form an incomparable gallery of colourful types: including, among others, the young Copernicus, proclaiming the truth of the heliocentric solar system.