When Steed pulls Mortimer (in his amnesiac state) in off the street, the door and the inside of the unit visible from the street do not come close to matching the door and the inside of the unit when they get inside.
At the opening of the tale, Mrs Peel fills in 12 down of her crossword as "anecdote". Steed is reminded of this on looking at the puzzle later - however in close-up Emma's answer is nowhere to be seen, and the completed squares on the grid spell gibberish words (and are occasionally numbers).