But Hanslet stared at the knife in silence, his brain a whirl of conflicting theories. If the Professor was correct in his assumption, Copperdock was a victim of the unknown assassin. How did this knife, which, as Whyland said, was exactly similar to those with which Tovey and Pargent had been killed, come into his possession? On the other hand, if Copperdock had been the murderer, what became of the Professor’s theory? Why should one of the jurymen wish to murder his colleagues? The problem became more complicated with every fresh discovery. “This blessed case would drive an archangel to drink,” he observed disgustedly, as he wrapped up the knife again and put it in his pocket. “Well, we’d better go across and see what young Copperdock has to say about this, eh, Whyland?” Chapter XX Mr. Ludgrove’s Invitation April gave place to May, and May to June, with no further development in the mystery which surrounded the Praed Street murders. The discovery of the knife in the pocket of Mr. Copperdock’s overcoat, combined with the fact that although Dr. Priestley and Mr. Ludgrove had each received a numbered counter, they had not so far been menaced by any particular danger, had convinced the police that the secret had died with Mr. Copperdock. A very careful examination of the handle showed that it bore his finger-marks, and his son, although he could not account for its presence where he had found it, was emphatic that it could not have been placed there since the night of his death. The Professor made no reference whatever to the case, either to Harold or to Hanslet. The latter during his infrequent visits to the house in Westbourne Terrace, made no reference to the case. He was becoming more and more convinced that the Professor’s interview with the Black Sailor had been a pure hallucination; that the Professor, having imagined the sequel to his theory of the jurymen, had somehow been under the illusion that the events of his imagination had actually taken place. In his own mind, however, he was by no means satisfied with the official view of the matter, of which Whyland was the principal exponent. It left so much to be explained, chiefly Copperdock’s motive, to say nothing of his methods. To begin with, how had he contrived to murder Mr. Tovey, when at the moment of the latter’s death he was sitting comfortably before his own fire? And, if the answer to this was that he had accomplices, who and where were they?