A young Polish diplomat turned cavalry officer at the outbreak of World War II, Karski joined the Polish underground movement in 1939 after ingeniously escaping from a Soviet detention camp. Most of the Polish officers held with him were later executed. Karski became a courier for the underground crossing enemy lines to serve as liaison between occupied Poland and the free world. Captured by the Gestapo in 1940 he was savagely tortured. Afraid that the Germans would extract secrets from him he slashed his wrists. But after the suicide attempt failed, he escaped from a hospital with the help of an underground commando team. His work had just begun. Karski, a Roman Catholic, developed a keen concern for the plight of the Jews under Nazi domination. In 1942 Jewish leaders asked him to carry a desperate message to Allied leaders: the news of Hitler's effort to exterminate the Jews of Europe. To be able to carry an authentic eyewitness report, Karski agreed to tour Warsaw's Jewish Ghetto in disguise. The suffering he saw there was only a prelude to the atrocities he witnessed when he later volunteered to be smuggled into a camp that was part of the Nazi murder machine. Carrying searing tales of inhumanity, Karski reached London in late 1942. He met secretly with top Allied officials, including British foreign secretary Anthony Eden, and with intellectuals like H.G. Wells and Arthur Koestler. Some reacted viscerally to his message. Others responded with disbelief or indifference. In July 1943, Karski traveled secretly to Washington, where he briefed President Roosevelt in a dramatic meeting. This fully documented account of Karski's myriad encounters discloses new information about how leaders in the West reacted to the Holocaust. Karski is the first definitive account of Jan Karski's mission, which was perhaps the most significant warning of the impending Holocaust to reach the free world.