You found yourself in an electrically lighted world of passages built in flashing steel, with floors of steel and ceilings of steel—­a world where the temperature was always 65 deg..  Every passage was separated from every other passage by steel grilles, and at intervals uniformed and gigantic officials wandered about with impassive, haughty faces—­faces that indicated a sublime confidence in the safety of the multifarious riches committed to their care.  You might have guessed yourself in the fell grip of the Inquisition.  As a fact, you were in something far more fell.  You were in a vast chamber of steel, and that chamber was itself enclosed on all sides by three feet of solid concrete.  No thief could tunnel or mine you without first getting through the District Railway on the one hand, or the main drainage system of London on the other.  No thief could rifle you by means of duplicate keys, for no vault and no safe could be opened except in the presence of the head guardian, who possessed a key without which the renter’s key was useless.  No tricks could be played with the gas, because there was no gas, and the electric light could only be turned off or on from the top of the lift-well.

Now, it was a singular thing that when Simon Shawn, having proved his identity and his mission at the lift, arrived at the entrance to the Safe Deposit, he discovered the great steel door ajar, and no door-guardian in the leather chair where a door-guardian always sat.  This condition of affairs did not affect the essential impregnability of any individual vault or safe, but, nevertheless, it was singular.

Simon walked straight in.

‘There’s no one at the door,’ he said to the patrol, whom he met in the main passage.  ’I want to see Mr. Hugo at once.  He’s down here somewhere, or he’s been here.’

‘Yes, Mr. Shawn,’ said the patrol politely; ’I did see Mr. Hugo here about an hour or so ago.  I’ll ask Mr. Brown.  Will you step into the waiting-room?’

Half-way along the main corridor was a large room, whose steel walls were masked by tapestries, where renters could examine their treasures on marble tables.  It was empty when Simon went in.  The patrol carefully closed the door on him, and then in a moment came back to say that Mr. Brown was not in his office, and had probably gone out to lunch, the hour being noon.

‘Where did you see Mr. Hugo?’ Simon asked, hurrying out of the room in a state of considerable agitation.

‘I saw him just here, sir,’ said the patrol, turning down a short side corridor—­the grille was unfastened—­and stopping before a door numbered thirty-nine.  ’He was talking to Mr. Brown, and the door of the vault was open.’

‘That must be Mr. Polycarp’s vault,’ Simon observed; and then he started, and put his ear against the door.  ‘Listen!’ he exclaimed to the patrol.  ‘Can’t you hear anything inside?’

And the patrol also put his ear to the steel face of the door.