After awhile Martha, the scientist's aged servant, appeared in the doorway.
"Mr. Mallory and a gentleman, sir."
"Let them come in," said The Thinking Machine. "Mr. Curtis," and he turned to him gravely, "Mr. Reid is here. I sent for him as if at your request to ask him two questions. If he answers those questions, as I believe he will, I can demonstrate that you are not guilty of and have no connection with the murder of Miss Melrose. Let me ask these questions, without any hint or remark from you as to what the answer must be. Are you willing?"
"I am," replied Curtis. His face was white, but his voice was firm.
Detective Mallory, whom Curtis didn't know, and Charles Reid entered the room. Both looked about curiously. Mallory nodded brusquely at Hatch. Reid looked at Curtis and Curtis looked away.
"Mr. Reid," said The Thinking Machine, without any preliminary, "Mr. Curtis tells me that the knife used to kill Miss Melrose was your property. Is that so?" he demanded quickly, as Curtis faced about wonderingly.
"No," thundered Reid, fiercely. "Is it Mr. Curtis's knife?" asked The Thinking Machine.
"Yes," flashed Reid. "It's a part of his auto kit."
Curtis started to speak; The Thinking Machine waved his hand toward him. Detective Mallory caught the gesture and understood that Jack Curtis was his prisoner for murder.