The Cristal Stopper by Maurice LeBlanc

The moment Lupin had finished lunch, he at once and, so to speak, without transition, recovered all his mastery and authority. The time for joking was past; and he must no longer yield to his love of astonishing people with claptrap and conjuring tricks. Now that he had discovered the crystal stopper in the hiding-place which he had guessed with absolute certainty, now that he possessed the list of the Twenty-seven, it became a question of playing off the last game of the rubber without delay.

It was child's play, no doubt, and what remained to be done presented no difficulty. Nevertheless, it was essential that he should perform these final actions with promptness, decision and infallible perspicacity. The smallest blunder was irretrievable. Lupin knew this; but his strangely lucid brain had allowed for every contingency. And the movements and words which he was now about to make and utter were all fully prepared and matured: