The film opens with the assassination of Congolese Prime Minister Patrice Lumumba and the outbreak of civil war. As the mineral rich State of Katanga secedes under the leadership of Moise Tshombe, United Nations Secretary General Dag Hammarskjöld assigns Conor Cruise O'Brien to head up a UN peacekeeping mission. Privately, Hammarskjöld tells O'Brien that the Katanga crisis could potentially trigger World War III and orders the Irish diplomat to take offensive action.