This study examines the unprecedented role played by a nongovernmental organization, the Henry Dunant Centre for Humanitarian Dialogue (HDC), in brokering negotiations and implementing an agreement reached between the Indonesian government and the armed Acehnese separatist movement GAM. The analysis tries to understand what caused the breakdown of the agreement, by looking at the strengths and weaknesses of a nongovernmental institution like HDC in mediating and then attempting to guide implementation of complex, risk-prone accords between battle-hardened adversaries.