Martin of Gfenn is the story of a young artist named Martin living in Zürich, Switzerland, in the mid-thirteenth century. Left by his father (a minor knight) with the Augustine Canons of St. Martin, Martin shows promise as an artist at a very young age. The Provost finds a teacher for Martin in the person of Michele, an Augustine Canon and artist from Verona, who has been sent to Zürich as punishment and penance. Michele teaches Martin everything about fresco painting, infusing him with his own passion for drawing, color and the plaster itself. After a few years, Michele is called back to Verona.
At nineteen, primed to begin his life as a master painter, Martin contracts leprosy. He is given the rite of separation and sent away from the Augustine Canons of St. Martin and told to go to the leper community of the Knights of St. Lazarus in the village of Gfenn, one day walk to the north. Unable to bear the thought of this, he goes in the other direction, to the city of Zürich.
As often happens in the early days of the disease of leprosy, Martin’s symptoms go into remission. Hoping this is a sign that he is healed or the diagnosis was mistaken, Martin builds a successful career as a painter on the streets of the swiftly growing city. After three years, at the moment his dream of painting the walls of Zürich’s great church, the Grossmünster, is about to be realized, his disease reappears with a vengeance. Martin soon knows he cannot remain in Zürich without being discovered. He leaves, resolved to finally go to the Lazarite Community at Gfenn.
On his journey to Gfenn, Martin suffers from the flu, and finds he cannot travel. He retreats into the forest of the Zürichberg (Zürich Mountain) which is between Zürich and Gfenn. Fascinated by the mysteries of the natural beauty around him, new and unfamiliar, he spends the summer as a Wild Man of the Woods, learning more about drawing and about himself. Finally, caught by some dogs belonging to boar hunters, Martin is discovered. He knows he cannot fight his fate any longer, and he makes his way to the small enclave of the Knights of Saint Lazarus, in the village of Gfenn.
Though he could not have known it, it is only when he accepts his condition that Martin can be who he really is. Believing it his destiny to paint a sanctuary, he undertakes the newly built chapel at the community of the Knights of St. Lazarus. The philosophical focus of the story is a look at Medieval Christianity from the perspective of Martin whose leprosy, youth, passion for painting and education have conspired to make him an early-day Christian humanist.