Rohmer decided to describe a seemingly impossible murder and then solve it as he continued to write. By the end of the third chapter, he realized he had left no room for a solution and gave up. Meanwhile his agent had sold the story to Collier's for serialization and the first chapter had already been printed. Sax travelled to New York and holed up in a hotel to try and find a solution. He kept writing but could think of no way out. Unbelievably, he was visited by Harry Houdini who had underlined one sentence and told Rohmer how to explain the murder. The all important sentence is in chapter 3.