Samuel Copperdock, whom he had studied so carefully, did not appear to him to be a deliberate criminal. He was not of the type which harbours revenge, and he did not seem either clever or painstaking enough to work out the details of a premeditated murder. Although, if it were true that he had formed a design to marry Mrs. Tovey, the murder of Mr. Tovey might be said to be advantageous to him, it was inconceivable that he had had any hand in it. He could not have struck the blow himself, and, since he was not a rich man, it was difficult to see what inducement he could offer to a hired assassin. In all human probability, Mr. Copperdock was innocent of the murder of James Tovey. But, on the other hand, this murder, followed so closely by the mysterious death of his other acquaintance, Colburn, had made a great impression upon him. He had thought and talked of little else, and, as it happened, he had known every detail. He had seen the knife with which James Tovey had been killed; he, in common with very few others, had known of the receipt of the marked counters. Suppose that the crimes had had such a powerful effect upon his imagination that he had felt an irresistible impulse to imitate them? Such things were known, were in fact a commonplace of the criminal psychologists. Upon this assumption, the rest was easy. Mr. Copperdock had learnt by some accident that this man Richard Pargent would arrive at Paddington at 4.55 on Saturday, and had selected him as a likely victim. His imitative faculty fully developed, he had sent him the numbered counter, and had purchased a knife similar to the one which he had already seen. Then, just before the train was due, he had left his shop, met his victim, committed the crime, had a drink to steady his nerves, and then come home. The theory was plausible, but Inspector Whyland knew well enough that so far he had not a fragment of real evidence with which to support it. But, unless he were to adopt the suggestion of Mr. Ludgrove, that some homicidal maniac was responsible, Whyland could see no alternative. The lack of motive was so extraordinarily puzzling. The murders had been utterly purposeless, and the only possible theory could be one which took full account of this fact. And then again, how account for the despatch of the numbered counters? If the murders had been inspired by irresponsible impulse, what had been their object?