"Knife?"
"The knife."
"I've lost the key."
"Lost the key? of what?"
"I put it in a wardrobe drawer with my--my things, and locked it, and, somehow, I lost the key."
"I don't quite follow. Do you mean that, having locked up my knife in a drawer with some other articles, you have mislaid the key of the lock?"
"Yes, that's what I mean."
"Then in that case, you had better break that lock open at the earliest possible moment."
"Why?"
"The answer's obvious, in order that you may hand me back my knife. If I'm to be the criminal it will never do for my knife to be found in your possession. It would involve all sorts of difficulties which we might neither of us find it easy to get over. Give me the knife. I will hide it somewhere on my own premises, where I'll take care that, at the proper moment, it is found. Properly managed, that knife ought to make my guilt as plain as the noonday sun; mismanaged, the affair might assume quite a different complexion."