The Democratic Republic of the Congo is a former Belgian colony in West Africa whose people suffered horribly under their rulers before independence in 1960, after which years of misrule and conflict left the country with millions of dead and a legacy of systematic mistreatment. Viewers will not learn much of this from watching Jacques Sarasin's documentary On the Rumba River, though they will certainly be provided with an eye-opening view into the spirit of the Congolese people (for which there should be a better word than "indominatable," but none comes to mind). Instead, they will be treated to the sight of Congolese singer Antone Kolosoy—aka "Wendo," or "Papa Wendo"—who was nearly 80 at the time of filming in 2004 and yet expresses the musical vitality and charm of a seasoned teenager.

Sarasin (I'll Sing for You) is an unobtrusive type of documentarian, the kind who would rather hang back and let his subjects weave their spells instead of creating it for them. With little interest for elaborate scene-setting or backgrounding, On the Rumba River unfolds casually, from its gorgeous opening sequence where a stationary camera captures first an open vista and then a slow-moving passenger train barnacled with shouting and waving passengers. The legendary Papa Wendo is first presented in a moving segment where he and a band perform "Marie-Louise," the breakthrough song from the 1940s (he began performing in 1936) that first established him as a star.

That performance and others that follow are of course the primary reason for viewing this film, which takes pains to paint the landscape that this music grew out of without letting it move too strongly into the foreground. Wendo's voice is a mellifluous thing, alternating between velvety and rough tones, tripping lightly over the band's liquid syncopations and seductive beats. Over the course of this short and slow-moving film, Sarasin tips in interviews with other aging musician friends of Wendo’s as he goes about trying to get the band back together.

Following a couple of comic interludes—Wendo's wife griping at him to go out and find work instead of sleeping under a tree, Wendo driving in circles through a town trying to find his old saxophone player—the film spends more time in Wendo's ad-hoc performance space. Although the details of what's going on are kept quite fuzzy for most of the film (Is there a particular show they're rehearsing for? Who is everybody?), those things become quite irrelevant once the throng of horn-players, backup singers, guitarists, and dancers start laying down their rhythms as a carpet for Wendo to glide over.

There are certainly some frustrating aspects to On the Rumba River, as much of Wendo's biography is left to only the most elliptic comments about the past oppression from the government and religious leaders. Also, in some of its later segments, the mellow pacing becomes practically glacial. But the film remains a beautiful and warm-hearted portrait of a singer who seems at times the beating heart of a country.