“First, bear it in mind that the crime was planned and undertaken by the two of them⁠—Knighton and Ada Mason, working together. Knighton was in Paris that day on your business. He boarded the train somewhere on its way round the ceinture . Mrs. Kettering would be surprised, but she would be quite unsuspicious. Perhaps he draws her attention to something out of the window, and as she turns to look he slips the cord round her neck⁠—and the whole thing is over in a second or two. The door of the compartment is locked, and he and Ada Mason set to work. They strip off the dead woman’s outer clothes. Mason and Knighton roll the body up in a rug and put it on the seat in the adjoining compartment amongst the bags and suitcases. Knighton drops off the train, taking the jewel-case containing the rubies with him. Since the crime is not supposed to have been committed until nearly twelve hours later he is perfectly safe, and his evidence and the supposed Mrs. Kettering’s words to the conductor will provide a perfect alibi for his accomplice.