John Halliday

In the short story The Lady on the Stairs (later, chapters 5 and 6 of The Big Four), John Halliday was an English scientist. His research related to a method of concentrating wireless energy so that a powerful beam could be focused on a given spot, for example, in a weapon. He had read a paper on this before the British Association. He had been greeted with scepticism but persisted in his work, claiming that he was on the eve of success in his experiments. While visiting colleagues in Paris, Halliday was kidnapped by "The Big Four" until Poirot secured his release.