“Richard Negus committed suicide,” I heard myself declare. “He must have. He tried to make it look like murder—the same pattern as the other two, so that we would suspect the same killer—but he had to lock his door from the inside. Then he hid the key behind a fireplace tile to make it look as if the murderer had taken it, and opened a window to its full extent. If the hidden key was ever found, we would have wondered, as we did, why the murderer chose to lock the door from the inside, hide the key in the room and escape via the window, but we would still have believed there was a murderer. That was all that mattered to Negus. Whereas if the window was shut and by some chance the key was found, we would draw the only possible conclusion: that Richard Negus had taken his own life. He couldn’t risk our arriving at that conclusion—do you see? If we did, then the framing of Nancy Ducane for all three deaths would fail. We would be more likely to assume that Negus killed Harriet Sippel and Ida Gransbury before killing himself.”

“Yes,” said Jennie. “I think you are right.”

“The different positioning of the cufflink . . .” Poirot murmured before raising his eyebrows at me, indicating that he wished me to continue.

I said, “The cufflink was close to Negus’s throat because his death convulsions from the poison caused his mouth to open. He had carefully positioned himself in a straight line on the floor and placed the cufflink between his lips, but it fell to the back of his mouth. Unlike Harriet Sippel and Ida Gransbury, Richard Negus did not have a killer present when he died, and so the cufflink could not be carefully positioned in the agreed place.”

“Mademoiselle Jennie, you believe that Mr. Negus would swallow the poison, lie down and die without first attempting to discover why you had failed to arrive at the hotel?” Poirot asked her.

“I did not think he would, until I read of his death in the newspaper.”

“Ah.” Poirot’s expression was unreadable.

“For so long, Richard had been expecting to die on that Thursday night, looking forward to the end of his guilt and torment after so many years,” said Jennie. “I believe that all he wanted, once he arrived at the Bloxham, was for it to be over for him, and so, when I did not arrive to kill him as planned, he did it himself.”

“Thank you, mademoiselle.” Poirot rose to his feet. He wobbled a little to find his balance after so long in a seated position.

“What will happen to me, Monsieur Poirot?”

“Please stay here in this house until I or Mr. Catchpool return with more information. If you make the mistake of running away a second time, things will go very badly for you.”