Rose and Samuel Sayer (Katherine Hepburn and Robert Morley) are a brother/sister missionary team in Africa. Charlie Allnut (Humphrey Bogart) delivers their mail, supplies, and news of the outside world. It's 1914, and World War I has already started in Europe. The Germans are invading parts of Africa, but the Sayers won't leave and are eventually found by the Germans. Samuel dies. Charlie convinces prim and proper Rose to leave with him on his boat "The African Queen". He warns her of a German ship guarding an area they will have to pass through, but Rose says they'll turn the boat into a torpedo and blow up the German ship. On the trip down river, the couple deal with rapids, a German fort, and boat trouble, but they also fall in love. They outfit the Queen to blow up the German ship, but before it does, they are captured by the Germans. The captain marries them before the ship hits a floating chunk of the Queen and explodes. Charlie and Rose, now married, swim away.