"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."

We stared at one another blankly. Poirot had walked over to the
mantel-piece. He was outwardly calm, but I noticed his hands,
which from long force of habit were mechanically straightening
the spill vases on the mantel-piece, were shaking violently.

"See here, it was like this," he said at last. "There was
something in that case--some piece of evidence, slight in itself
perhaps, but still enough of a clue to connect the murderer with
the crime. It was vital to him that it should be destroyed
before it was discovered and its significance appreciated.
Therefore, he took the risk, the great risk, of coming in here.
Finding the case locked, he was obliged to force it, thus
betraying his presence. For him to take that risk, it must have
been something of great importance."

"But what was it?"

"Ah!" cried Poirot, with a gesture of anger. "That, I do not
know! A document of some kind, without doubt, possibly the scrap