She left us a moment later, visibly relieved.

Scarcely had she gone when Craig, stuffing the letters into his pocket unread, seized his hat, and a moment later was striding along toward the museum with his habitual rapid, abstracted step which told me that he sensed a mystery.

In the museum we met Doctor Bernardo, a man slightly older than Northrop, with whom he had been very intimate.  He had just arrived and was already deeply immersed in the study of some new and beautiful colored plates from the National Museum of Mexico City.

“Do you remember seeing Northrop here yesterday afternoon?” greeted Craig, without explaining what had happened.

“Yes,” he answered promptly.  “I was here with him until very late.  At least, he was in his own room, working hard, when I left.”

“Did you see him go?”

“Why—­er—­no,” replied Bernardo, as if that were a new idea.  “I left him here—­at least, I didn’t see him go out.”

Kennedy tried the door of Northrop’s room, which was at the far end, in a corner, and communicated with the hall only through the main floor of the museum.  It was locked.  A pass-key from the janitor quickly opened it.

Such a sight as greeted us, I shall never forget.  There, in his big desk-chair, sat Northrop, absolutely rigid, the most horribly contorted look on his features that I have ever seen—­half of pain, half of fear, as if of something nameless.

Kennedy bent over.  His hands were cold.

Northrop had been dead at least twelve hours, perhaps longer.  All night the deserted museum had guarded its terrible secret.

As Craig peered into his face, he saw, in the fleshy part of the neck, just below the left ear, a round red mark, with just a drop or two of now black coagulated blood in the center.  All around we could see a vast amount of miscellaneous stuff, partly unpacked, partly just opened, and waiting to be taken out of the wrappings by the now motionless hands.

“I suppose you are more or less familiar with what Northrop brought back?” asked Kennedy of Bernardo, running his eye over the material in the room.

“Yes, reasonably,” answered Bernardo.  “Before the cases arrived from the wharf, he told me in detail what he had managed to bring up with him.”

“I wish, then, that you would look it over and see if there is anything missing,” requested Craig, already himself busy in going over the room for other evidence.

Doctor Bernardo hastily began taking a mental inventory of the stuff.  While they worked, I tried vainly to frame some theory which would explain the startling facts we had so suddenly discovered.

Mitla, I knew, was south of the city of Oaxaca, and there, in its ruined palaces, was the crowning achievement of the old Zapotec kings.  No ruins in America were more elaborately ornamented or richer in lore for the archeologist.

Northrop had brought up porphyry blocks with quaint grecques and much hieroglyphic painting.  Already unpacked were half a dozen copper axes, some of the first of that particular style that had ever been brought to the United States.  Besides the sculptured stones and the mosaics were jugs, cups, vases, little gods, sacrificial stones—­enough, almost, to equip a new alcove in the museum.