On a fall day in 1928, a window was left open in a London laboratory, letting in a cool breeze. Carried on that breeze were microscopic spores of mold, tiny particles that fell gently onto a work surface covered with open Petri dishes culturing Staphylococcus bacteria. One spore landed on the rich culture medium of a dish and began to grow, contaminating the experiment in progress. This contamination, to the surprise of the scientist when he returned to check on his experiment, was peculiar. The mold had not simply grown, it had also destroyed all the bacteria around it, leaving a clear boundary all around its perimeter. The scientist was Alexander Flemming, and his determination to find out what was going on in this peculiar, unexpected, serendipitous mistake would lead to the world-changing discovery of antibiotics.