In the future, the world is devasted by an unknown and lethal virus. This virus has wiped out most of the population of earth. Only 1% of the population remains in 2035. A man is sent back in the past to find out the source of this man-made virus. Apparently, the virus has spread by a group of 12 monkeys. He has to locate the virus before it mutates. Will the man be able to locate the source and eliminate it in time to change the future?