There was, in the entire aspect of the room, something very grim and dreadful.  An atmosphere of tragic mystery enveloped the most commonplace objects; and sinister suggestions lurked in the most familiar appearances.  Especially impressive was the air of suspense—­of ordinary, every-day life suddenly arrested—­cut short in the twinkling of an eye.  The electric lamps, still burning dim and red, though the summer sunshine streamed in through the windows; the half-emptied tumbler and open book by the empty chair, had each its whispered message of swift and sudden disaster, as had the hushed voices and stealthy movements of the waiting men, and, above all, an awesome shape that was but a few hours since a living man, and that now sprawled, prone and motionless, on the floor.

“This is a mysterious affair,” observed Inspector Badger, breaking the silence at length, “though it is clear enough up to a certain point.  The body tells its own story.”

We stepped across and looked down at the corpse.  It was that of a somewhat elderly man, and lay, on an open space of floor before the fireplace, face downwards, with the arms extended.  The slender hilt of a dagger projected from the back below the left shoulder, and, with the exception of a trace of blood upon the lips, this was the only indication of the mode of death.  A little way from the body a clock-key lay on the carpet, and, glancing up at the clock on the mantelpiece, I perceived that the glass front was open.

“You see,” pursued the inspector, noting my glance, “he was standing in front of the fireplace, winding the clock.  Then the murderer stole up behind him—­the noise of the turning key must have covered his movements—­and stabbed him.  And you see, from the position of the dagger on the left side of the back, that the murderer must have been left-handed.  That is all clear enough.  What is not clear is how he got in, and how he got out again.”

“The body has not been moved, I suppose,” said Thorndyke.

“No.  We sent for Dr. Egerton, the police-surgeon, and he certified that the man was dead.  He will be back presently to see you and arrange about the post-mortem.”

“Then,” said Thorndyke, “we will not disturb the body till he comes, except to take the temperature and dust the dagger-hilt.”

He took from his bag a long, registering chemical thermometer and an insufflator or powder-blower.  The former he introduced under the dead man’s clothing against the abdomen, and with the latter blew a stream of fine yellow powder on to the black leather handle of the dagger.  Inspector Badger stooped eagerly to examine the handle, as Thorndyke blew away the powder that had settled evenly on the surface.

“No finger-prints,” said he, in a disappointed tone.  “He must have worn gloves.  But that inscription gives a pretty broad hint.”

He pointed, as he spoke, to the metal guard of the dagger, on which was engraved, in clumsy lettering, the single word, “TRADITORE.”