In August/September 1914, Rose Sayer, a 33-year-old British woman, is the companion and housekeeper of her brother Samuel, a Methodist missionary in German East Africa.

[N 1] World War I has begun, and the German Schutztruppe commander of the area has conscripted all the natives; the village is deserted, and only Rose and her brother, who is dying, remain.

He is the mechanic and skipper of the African Queen, a steam-powered launch, owned by a Belgian mining corporation, that plies the upper reaches of the Ulanga River.

She realizes that the main German defence against a British attack by water in the area is a gunboat, Königin Luise, which guards the fictional Lake Wittelsbach[1] into which the Ulanga feeds.

The descent to the lake poses three main problems: passing the German-held town of Shona; navigating heavy rapids and cataracts; and getting through the river delta.

The German commander assumes that the launch is coming in to surrender (because he believes no boat could pass the rapids downriver from the town, so Shona is the only possible destination).

Tormented by biting insects, sickened by malaria, and wracked by the heat and thunderstorms, they drag the launch through miles of reeds and water-grass with their boat-hooks, occasionally diving to cut fallen logs out of their way.

They fire up the engine and set out on the attack, but halfway to their target a storm sweeps up and overwhelms them; the launch sinks, and Rose and Allnutt have to swim for safety.

Both refuse to say how they came to the lake, but the captain sees "African Queen" written on Rose's life-saver and deduces that they must be the mechanic and the missionary's sister from the missing launch.

He decides it would be uncivilised to execute them, so he flies a flag of truce and delivers them to the British naval commander, who dismissively sends them to separate tents under guard while he takes his newly arrived reinforcements out to sink the Königin Luise.

The novel was made into a film in 1951: The African Queen, starring Humphrey Bogart as Charlie Allnutt and Katharine Hepburn as Rose Sayer.

Intended as a pilot for a television series following the further adventures of the Alnutts, it stars Warren Oates as Charlie and Mariette Hartley as Rose.