Surrounded by books, Jack Preger leads an ascetic life in a room on the roof of his school. This tireless doctor has roamed the slums of Calcutta for 35 years. Through his perseverance and radical life choice, he initiated a movement that has become global: street medicine. At 83 years of age, he has accepted for the first time to speak in front of a camera, thus opening the personal book of his exceptional life, that of a secular saint.