Already slight hints, thin rumours of what was being done in the laboratories of Regent's Park, were beginning to filter through the most important scientific circles. A paper read by Sir William at the British Association, a guarded article contributed to the _Nineteenth Century_, propounding some most daring theories as to the real action of the mind, had already prepared some of the shrewdest brains in Europe for a possible revelation of something stupendously startling in the realms of scientific achievement. A few keen and brilliant brains had realized, if Sir William was right, even in these preliminary conclusions, whither the conclusions tended. Lesser scientists who could not see so far, knew nothing. The man in the street was only aware that the great scientist had been working for years upon abstruse problems which had no interest for him whatever. But, nevertheless, in the highest circles, there was an indubitable stir and rumour. Yes! But little now remained to be done before absolute perfection of the invention was obtained. A few more experiments, more delicate and decisive than any that had gone before, still remained to be made. The apparatus itself was completed. Its working under certain conditions was certain. It was still necessary, however, to test it by means of continuous experiments upon a living human brain. During the last year of their work, Gouldesbrough and Wilson Guest had begun to realize this last necessity with increasing conviction. They saw that the coping-stone of the marvellous edifice which they had slowly built up through the years, was now resolving itself into this, and this alone. Neither had said as much to each other in so many words, until some four months ago. Then, upon one memorable night, when, excited by drink to an unusual freedom and openness of speech, Guest had voiced the unspoken thought of his master and himself. A human brain, a living human brain, in a living human body was an absolute and final requirement. There were not wanting, there never have been wanting, scientific enthusiasts who will submit themselves to experiment. But in this case a voluntary subject was impossible, for reasons which will presently appear. It became a definite problem with the two men as to how, and by what means, they should obtain a living creature who should be absolutely subject to their will. And then chance had provided Sir William with the unique opportunity. He had seen his way to rid himself of a hated rival, and to provide a subject for experiment at one and the same time. He had not hesitated. Brains so far removed from the ordinary sphere of humanity as his never hesitate at anything. Guy Rathbone had disappeared. The motor stopped at the door in the great, grim wall which surrounded Sir William's house. He said good-night to the chauffeur who looked after his two cars at a garage some half-a-mile away, and opened the wicket with his key.