"It Rained All Night the Day I Left" is a story about two charming gunrunners, Robert Talbot and Leopold Garcia, who met in Rhodesia and became friends and partners. Their latest venture takes them to a small desert place in Africa, where they are ambushed and mugged by guards.
They soon discover that they are on the property of the Colonel, a tough and good-looking widow of a wealthy white ranch owner who fought alongside the real-life Nazi German general Rommel in WWII. The Colonel blames the local poor black population for her husband's murder and plans to cut off the water supply to the town as an act of vengeance.
The government threatens to nationalize her land and throw her out, so she hires Bob and Leo to help her. However, the two gunrunners do not agree with punishing the townsfolk and instead decide to investigate the late husband's shady competitor, Killian, who plans to marry the Colonel's daughter, Suzanna, in an arranged marriage.
As the story unfolds, the Colonel falls for Leo and Suzanna falls for Bob. When the Colonel proposes marriage to Leo and asks Bob to marry her daughter to form a family, Leo is interested but Bob gets cold feet.