Documentary portrait of Armand Frappier, an internationally renowned Quebec microbiologist, distinguished violinist and great humanist. At 87, he rummages through his archives, rereads his correspondence and relives his fight against an infinitely small killer: the microbe. This film recalls his talents as an initiator ― setting up major vaccination campaigns against tuberculosis, among other things ― as an entrepreneur through the creation of a formidable Quebec industry of organic products, as an educator through the founding of the School of Public Hygiene at the University of Montreal, and finally, as a professor.