One night in Beirut in September 1982, while Israeli soldiers secured the area, Christian militia members entered the refugee camps of Sabra and Shatila and began to massacre hundreds, if not thousands, of Palestinians. Ari Folman was one of those Israeli soldiers, but for more than twenty years he remembered nothing of that night or of the weeks leading up to it. Then came a friend's disturbing dream, and with it Folman's need to excavate the truth of the war in Lebanon and answer the crucial question: what was he doing during the hours of slaughter?