Detective Murdoch investigate the shooting death of inventor Karl Schreyer who was shot at an inventor's convention. He was very much disliked by his fellow inventors who accused him of stealing their ideas for his own use. He had contacted Murdoch after receiving a threatening note and he was there when Schreyer was shot giving his thank you speech for winning the Eaton Prize for most commercially viable invention in this case, a vacuum cleaner. Murdoch's biggest problem is to figure out just how an assassin could shoot him without being seen. While the evidence points to other inventors as responsible for the murder, an invention by Alexander Graham Bell provides the solution to the crime. Meanwhile, Constable Crabtree tries to commercialize some of Murdoch's inventions.