The Lone Wolf by Louis Joseph Vance

Now when Lanyard had locked the door, he told himself that the gruesome peace of those two bedchambers was ensured, barring mischance, for as long as the drug continued to hold dominion over the American; and he felt justified in reckoning that period apt to be tolerably protracted; while not before noon at earliest would any hôtelier who knew his business permit the rest of an Anglo-Saxon guest to be disturbed -- lacking, that is, definite instructions to the contrary.

For a full minute after withdrawing the key the adventurer stood at alert attention; but the heavy silence of that sinister old rookery sang in his ears untroubled by any untoward sound.