Horace Danby was a meticulous planner who carefully studied the house at Shotover Grange, including its rooms, electric wiring, paths, and the timing when the house would be empty. He even knew the name of the dog and the value of the jewels in the safe. However, he faltered because he failed to gather enough information about the real occupants of the house and was completely deceived by a lady he met there. He trusted her blindly, did not suspect her to be a thief, and got scared when confronted by her. In his haste to comply with her demands, he opened the safe without wearing gloves, leaving fingerprints that led to his arrest. His careful planning was undone by his lack of suspicion and presence of mind when dealing with the lady, which was his critical mistake
. In summary, Horace's mistake was his failure to verify the identity and intentions of the occupants, especially the lady, and his lapse in caution by leaving fingerprints, which ultimately caused him to be caught despite his meticulous planning.
