It is about a man who was victim of a shipwreck to which he was the only survivor. Coming from a far-away country that doesn't speak English, he does not understand anybody (nor anyone can understand him) and therefore he is taken by a madman. Amy Foster, a sweet, kind young girl, sees that he means no harm and then she helps him by giving him some food. After that moment starts Yanko's love for her, calling her “charitable lady”.
It is said that this book is somewhat autobiographical, with its author (Joseph Conrad) being Yanko. Conrad was Polish, but he got a British nationality, nonetheless, he was always considered a Polish.