Set on the Upper Sepik River in New Guinea, this film records the day-to-day experiences of Kiap (one-man representative of the Australian government in regional areas) Barry Downes as he patrols an area that in 1963 had only recently been brought under control from headhunters. As well as being a record of the role of the colonial administration, Along the Sepik offers insights into some tribal communities' cultures through depictions of their spirit houses and traditional 'sing sing' ceremonies. Downes investigates a murder, and the culprit is caught and tried by a magistrate in a jungle courthouse under the Australian flag, on the edge of the Sepik River. Australian patrol officers and their men operated under rugged conditions to bring western law and order to this remote area. The film also portrays some of the impact the colonial government had on regional, traditional communities.