The title character of Sanders of the River, Commissioner R.G. Sanders (Leslie Banks), is a British officer who has picked up the white man’s burden and made Nigeria a better place for the Africans who populate it. We know they are happy, because they are always singing. The British do not sing, however, because running an empire is serious business.
Bosambo (Paul Robeson) is a good African chieftain who loves being ruled by Sanders and the British Empire. He sings a lot. Mofolaba (Tony Wane) is an evil African chieftain who hates being ruled by Sanders and the British Empire. He doesn’t sing at all.
When Sanders goes on vacation, Mofolaba spreads a rumor that Sanders is dead. Apparently there is a cult of personality surrounding Sanders, because the place just falls apart as a result. We see lots of animals running about, so even they are upset.
War breaks out, and Sanders has to return. While he was gone, a couple of smugglers had been selling gin and rifles to the natives, which is against the law. But the rifles don’t seem to do the natives any good, because they continue to use spears. Bosambo is captured by Mofolaba. As the boat Sanders is on races to save Bosambo, an officer commands an African worker who is operating the boiler to put more wood on the fire for more speed. The African replies that the boiler will blow. But the British officer is not cowed by mere physics, and he contemptuously dismisses the warning. The boiler backs down and humbly submits to British authority, just like everything else.
Thanks to British assistance, Bosambo is able to kill Mofolaba. Sanders names him King of the Peoples of the River, and they all live happily ever after.