"But now a hitch occurs. Mrs. Inglethorp does not take her medicine that night. The broken bell, Cynthia's absence-- arranged by Inglethorp through his wife--all these are wasted. And then--he makes his slip.
"Mrs. Inglethorp is out, and he sits down to write to his accomplice, who, he fears, may be in a panic at the nonsuccess of their plan. It is probable that Mrs. Inglethorp returned earlier than he expected. Caught in the act, and somewhat flurried he hastily shuts and locks his desk. He fears that if he remains in the room he may have to open it again, and that Mrs. Inglethorp might catch sight of the letter before he could snatch it up. So he goes out and walks in the woods, little dreaming that Mrs. Inglethorp will open his desk, and discover the incriminating document.
"But this, as we know, is what happened. Mrs. Inglethorp reads it, and becomes aware of the perfidy of her husband and Evelyn Howard, though, unfortunately, the sentence about the bromides conveys no warning to her mind. She knows that she is in danger--but is ignorant of where the danger lies. She decides to say nothing to her husband, but sits down and writes to her solicitor, asking him to come on the morrow, and she also determines to destroy immediately the will which she has just made. She keeps the fatal letter."
"It was to discover that letter, then, that her husband forced the lock of the despatch-case?"
"Yes, and from the enormous risk he ran we can see how fully he realized its importance. That letter excepted, there was absolutely nothing to connect him with the crime."
"There's only one thing I can't make out, why didn't he destroy it at once when he got hold of it?"
"Because he did not dare take the biggest risk of all--that of keeping it on his own person."
"I don't understand."
"Look at it from his point of view. I have discovered that there were only five short minutes in which he could have taken it--the five minutes immediately before our own arrival on the scene, for before that time Annie was brushing the stairs, and would have seen anyone who passed going to the right wing. Figure to yourself the scene! He enters the room, unlocking the door by means of one of the other doorkeys--they were all much alike. He hurries to the despatch-case--it is locked, and the keys are nowhere to be seen. That is a terrible blow to him, for it means that his presence in the room cannot be concealed as he had hoped. But he sees clearly that everything must be risked for the sake of that damning piece of evidence. Quickly, he forces the lock with a penknife, and turns over the papers until he finds what he is looking for.