London was still recovering from the devastation of World War II when another disaster hit: for five long days in December 1952, a killer smog held the city firmly in its grip and refused to let go. Day became night, mass transit ground to a halt, criminals roamed the streets, and some 12,000 people died from the poisonous air. But in the chaotic aftermath, another killer was stalking the streets, using the fog as a cloak for his crimes.