“ Milles tonnerres! ” cried Poirot, dumbfounded. “And I⁠—who have both the keys in my pocket!” He flung himself upon the case. Suddenly he stiffened. “ En voilà une affaire! This lock has been forced.”

“What?”

Poirot laid down the case again.

“But who forced it? Why should they? When? But the door was locked?” These exclamations burst from us disjointedly.

Poirot answered them categorically⁠—almost mechanically.

“Who? That is the question. Why? Ah, if I only knew. When? Since I was here an hour ago. As to the door being locked, it is a very ordinary lock. Probably any other of the doorkeys in this passage would fit it.”