about five o'clock
To which I retort that if two and two plus X make six , then to discover the unknown quantity is the simplest thing in the world . That a houseful of detectives missed it entirely was because they were busy trying to prove that two and two make four . The depression due to my visit to the hospital left me at the prospect of seeing Halsey again that night . It was about five o'clock when Liddy left me for a nap before dinner , having put me into a gray silk dressing-gown and a pair of slippers . I listened to her retreating footsteps , and as soon as she was safely below stairs , I went up to the trunk-room . The place had not been disturbed , and I proceeded at once to try to discover the entrance to the hidden room . The openings on either side , as I have said , showed nothing but perhaps three feet of brick wall .