The Square Circle is a 1982 novel by Daniel Carney. It was adapted as the 1985 film Wild Geese II. After the success of his novel, The Wild Geese (1977) (originally titled The Thin White Line), Carney was asked by producer Euan Lloyd to write a follow up. Lloyd had already turned The Thin White Line into the hit movie The Wild Geese, and was constantly being asked to make a sequel. At first Carney refused as he just couldn't come up with a premise for the story, Lloyd wouldn't be put off and suggested the theme could be the rescue of Rudolf Hess from Spandau Prison in West Berlin.