six o'clock
He might have kept the marked paper for future use , and , on the occasion of the robbery , pencilled a dated inscription on it , and slipped it into the safe as a sure means of diverting suspicion . All this was improbable in the highest degree , but then so was every other explanation of the crime ; and as to the unspeakable baseness of the deed , what action is too base for a gambler in difficulties ? I was so much excited and elated by my own ingenuity in having formed an intelligible and practicable theory of the crime , that I was now impatient to reach home that I might impart my news to Thorndyke and see how they affected him . But as I approached the centre of the town the fog grew so dense that all my attention was needed to enable me to thread my way safely through the traffic ; while the strange , deceptive aspect that it lent to familiar objects and the obliteration of landmarks made my progress so slow that it was already past six o'clock when I felt my way down Middle Temple Lane and crept through Crown Office Row towards my colleague 's chambers . On the doorstep I found Polton peering with anxious face into the blank expanse of yellow vapour . `` The Doctor 's late , sir , '' said he . `` Detained by the fog , I expect .