Why does Jimmy not meet Bob?
Jimmy Wells actually does meet Bob as promised twenty years ago when they parted at 'Big Joe' Brady's restaurant. Jimmy is the uniformed police officer who is introduced right at the beginning of the story "After Twenty Years." This happens to be Jimmy's regular beat now. He is doing his usual job of patrolling his beat, which includes trying all the doors of closed shops to make sure they are locked. He fully plans to meet Bob at the spot where 'Big Joe' Brady's used to be, but he is a few minutes early, so he is just doing his regular duty.
When Jimmy gets to the doorway of the hardware store where Bob is standing out of the rain, Bob doesn't recognize him for several reasons. For one thing, Jimmy is twenty years older and naturally would have changed a great deal with age. Furthermore, Jimmy is wearing a cop's blue uniform and cap, which would alter the picture Bob had retained of him in his mind. But most importantly, the neighborhood is very dark because all the businesses are closed. Jimmy only recognizes Bob because he expects to meet his old friend at that location. But he doesn't really know it is Bob until Bob lights a cigar. Bob has backed in into the doorway to keep dry and also to keep from getting his cigar wet. The night is dark, cold, drizzly and windy. It would be much easier to light a cigar in the shelter of the doorway.
Bob is obviously a great talker. He starts talking immediately when he sees a cop in front of him. He thinks the cop wants to look him over because he is standing in a dark doorway with no apparent reason for being there.
“It's all right, officer,” he said, reassuringly. “I'm just waiting for a friend. It's an appointment made twenty years ago. Sounds a little funny to you, doesn't it? Well, I'll explain if you'd like to make certain it's all straight. About that long ago there used to be a restaurant where this store stands— ‘Big Joe’ Brady's restaurant.”
Then when Bob lights his cigar, the author gives a brief description of his appearance.
The man in the doorway struck a match and lit his cigar. The light showed a pale, square-jawed face with keen eyes, and a little white scar near his right eyebrow. His scarf pin was a large diamond, oddly set.
When Bob lights his cigar, a process which a full minute with a cigar, Jimmy recognizes him as the man wanted by the Chicago police; and therefore he decides not to introduce himself as Jimmy Wells, who is there punctually to keep the appointment they made twenty years earlier. Jimmy lets Bob do most of the talking. He makes sure that Bob intends to stay there for at least another half-hour past their ten-o'clock appointment date, and then he goes to a close-by precinct station to find another officer to arrest his old friend. He has the plainclothes detective hand Bob a note after he has arrested him.
Bob: I was at the appointed place on time. When you struck the match to light your cigar I saw it was the face of the man wanted in Chicago. Somehow I couldn't do it myself, so I went around and got a plainclothesman to do the job. JIMMY.
The Chicago police had sent a "wire" about the man they apparently only knew as 'Silky' Bob. There was no way of sending a picture or even a sketch by telegraph wire, but they had obviously sent a full description. Jimmy recognized Bob as the wanted man by details in the telegram. Bob has a little white scar near his right eyebrow, which is the most telling detail. He wears a scarf pin which the telegram probably described in full. The pin consists of a large diamond "oddly set," probably with a lot of smaller stones arranged around it in a one-of-a-kind pattern. The telegram would also state that 'Silky' Bob always carries "a handsome watch, the lids of it set with small diamonds." Jimmy would recognize his old friend by his face, and he would recognize him as the wanted man by the little white scar, the diamond scarf pin, and the jeweled pocket watch. Naturally the telegram would include the usual specifications of race, gender, age, height, approximate weight, and customary clothing.