Jimgrim by Talbot Mundy

The entire wall slid sideways -- a mere screen that concealed an "icebox" door a pace or two beyond it. Light shone through a small round aperture in the door and we all stepped at once as close to the door as we could crowd ourselves to avoid being seen. After listening for about a minute Grim raised his eyes to the level of the hole and peered through. We could hear voices, but there was apparently no one on guard at the door. Grim put his arm through the hole -- groped -- tried to move a bolt of some sort -- failed and whispered to Jeff to try it. Jeff succeeded. The door swung inward on hinges that had been oiled quite recently.

We descended a stairway of plain deal boards into a vestibule of ancient masonry, that led into a gallery, which overhung an ancient burial chamber. On our way we passed the guardian of the door, apparently a Greek with a touch of Egypt in him, lying dead on his side with a knife between his shoulder-blades. He had been dead less than an hour -- perhaps less than thirty minutes. He had been slain with his own knife, drawn from the sheath in his red cotton sash.