The cop has a conversation with Bob, the man he sees. The man tells him he was waiting for his old friend he last saw 20 years ago (2-3).
A cop who Bob thinks is Jimmy comes up to him and they start walking while talking. Bob realizes that the man he is walking with is not Jimmy (3-4).
"'It sometimes changes a good man into a bad one,' said the tall man" (4).
Bob finds out he had been under arrest by the man he thought was Jimmy. Then the cop gives him a message from Jimmy- "'Bob: I was at the place on time. I saw the face of the man wanted by Chicago cops. I didn't want to arrest you myself. So I went and got another cop and sent him to do the job. JIMMY'" (4).