re-book. I thought it was queer
I hadn't seen him. And, what's more, that isn't Mr. Polycarp's vault at
all. Mr. Polycarp's vault is No. 37. This vault has been empty for
several weeks.'

'Then you have both the keys?' Simon demanded quickly.

'No, sir. It's very strange. There's only one key of No. 39 in the
key-safe, and it's the renter's key.'

'Then Mr. Brown must have the other.'

'I expect so. But he ought not to have. It's against rules,' said the
patrol. 'I know where he takes his lunch. I'll send for him.'

Simon put his ear again to the face of the door. The faint knocking had
ceased, but after a few seconds it recommenced.

'And suppose you don't find Mr. Brown?' he queried, still listening.

'Then that vault can't be opened. But never you fear, Mr. Shawn. I'll
have him here in three minutes. It's funny as he should have left
anybody in there by accident--and Mr. Hugo of all people in this
blessed world....'

The patrol's accents died away as he passed down the main corridor.

Within the next half-hour Simon, who had the rare virtue of being honest
with himself, was freely admitting, in the privacy of his own mind, that
the crisis had got beyond his power to grapple with it, and he had begun
to fear complications more dreadful than he dared to put into words. For
the patrol had failed to find Mr. Brown. Mr. Brown, head guardian of the
Safe Deposit, had disappeared. Nor was this all. A renter had come to
take his belongings from a safe in the third side-passage on the left,
and the sub-guardian imprisoned in that passage could not open the
grille between it and the main corridor. He had his key, but the key
would not turn in the glittering lock. The renter, too impatient to
wait, had departed very angrily at this excess of safety. Then it was
gradually discovered that every sub-guardian in every side-passage was
similarly imprisoned. Not a key in the entire place would turn. The
patrol rushed to the main door. The three keys had clearly been turned
while the door was opened, and the shot bolts prevented the door from
closing. This explained why the door was ajar, but it did not explain
the absence of the doorkeeper, who had apparently followed in the
footsteps of his chief, Mr. Brown.

'The time-lock! Someone must have set it!' cried the patrol to Shawn,
and the two hastened to the other end of the main corridor, where the
dial of the machine glistened under an electric lamp.

And all the sub-guar