故事发生在第一次世界大战时期的非洲。男主人公查尔斯·奥尔耐特是一名因失业而流落到非洲的矿山机械师，女主人公罗斯·塞耶是一位向非洲土人传道的教士。为了抵抗德国人，两人同乘一艘破旧的游艇－－“非洲皇后号”，沿河顺流而下。途中，这对个性迥然不同的中年男女不仅产生了真挚的爱情，而且还勇敢地击沉了一艘德国战舰……September 1914, news reaches the colony German Eastern Africa that Germany is at war, so Reverend Samuel Sayer became a hostile foreigner. German imperial troops burn down his mission; he is beaten and dies of fever. His well-educated, snobbish sister Rose Sayer buries him and leaves by the only available transport, the dilapidated river steamboat 'African Queen' of grumpy Charlie Allnut. As if a long difficult journey without any comfort weren't bad enough for such odd companions, she is determined to find a way to do their bit for the British war effort (and avenge her brother) and aims high, as God is obviously on their side: construct their own equipment, a torpedo and the converted steamboat, to take out a huge German warship, the Louisa, which is hard to find on the giant lake and first of all to reach, in fact as daunting an expedition as anyone attempted since the late adventurous explorer John Speakes, but she presses till Charlie accepts to steam up the Ulana, about to brave a German fort, raging rapids, very bloodthirsty parasites and the endlessly branching stream which seems to go nowhere but impenetrable swamps... Despite fierce rows and moral antagonism between a bossy devout abstentionist and a free-spirited libertine drunk loner, the two grow closer to each-other as their quest drags on...