September 1914, news reaches the colony German Eastern Africa that its motherland is at war, so Reverend Samuel Sayer became a hostile foreigner; German imperial troops burn down his mission, driving him mad- shortly after his well-educated, snooty sister Rose Sayer buries him and leaves by the only available transport, the crummy river steamboat 'African Queen' of grumpy boorish compatriot 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 revenge 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 nobody attempted since the late adventurous explorer John Speakes.