His mind began to move at length. The more he thought of it the more absolutely certain he was that he had fastened the door before leaving the house. True, the latch was only an ordinary one, and a key might easily have been made to fit it. As a matter of fact, David had two, one in reserve in case of accidents. The other was usually kept in a jewel-drawer of the dressing-table. Perhaps-- David went quietly upstairs. It was just possible that the murderer was in the house. But the closest search brought nothing to light. He pulled out the jewel-drawer in the dressing-table. The spare latchkey had gone! Here was something to go upon. Then there was a rumbling of an electric bell somewhere that set David's heart beating like a drum. The hall light streamed on a policeman in uniform and an inspector in a dark overcoat and a hard felt hat. On the pavement was a long shallow tray, which David recognised mechanically as the ambulance. "Something very serious, sir?" Inspector Marley asked, quietly. "I've brought the doctor with me." David nodded. Both the inspector and the doctor were acquaintances of his. He closed the door and led the way into the study. Just inside the conservatory and not far from the huddled figure lay David's new cigar-case. Doubtless, without knowing it, the owner had whisked it off the table when he had sprung the telephone. "'Um," Marley muttered. "Is this a clue, or yours, sir?" He lifted the case with its diamonds gleaming like stars on a dark night. David had forgotten all about it for the time, had forgotten where it came from, or that it contained L250 in bank-notes. "Not mine," he said. "I mean to say, of course, it is mine. A recent present. The shock of this discovery has deprived me of my senses pretty well." Marley laid the cigar-case on the table. It seemed strange to him, who could follow a tragedy calmly, that a man should forget his own property. Meanwhile Cross was bending over the body. David could see a face smooth like that of a woman. A quick little exclamation came from the doctor. "A drop of brandy here, and quick as possible," he commanded. "You don't mean to say," Steel began; "you don't--" Cross waved his arm, impatiently. The brandy was procured as speedily as possible. Steel, watching intently, fancied that he detected a slight flicker of the muscles of the white, stark face. "Bring the ambulance here," Cross said, curtly. "If we can get this poor chap to the hospital there is just a chance for him. Fortunately, we have not many yards to go." As far as elucidation went Marley naturally looked to Steel. "I should like to have your explanation, sir," he said, gravely.