How does the chase for "the second Montag" end? Also why must the authorities find a scapegoat? Finally why is Guy pleased about chicago?The book verision of this story
In Part Three of the novel, Granger takes out a portable television, and the group of hobo intellectuals watch the ensuing police chase. Granger mentions that Montag stumped the authorities, who cannot admit that they've failed to capture the criminal. It is important for the government to maintain an image of control, authority, and success, which is why they search for a scapegoat.
The men then watch closely as the authorities look for a scapegoat to blame for the crimes against the state. On the screen of the portable television, Montag and the men witness the Mechanical Hound chasing and injecting its procaine needle into the unsuspecting pedestrian, who happens to be wandering the streets at night. The innocent pedestrian is caught by surprise and left incapacitated by the Mechanical Hound's injection.
The police chase immediately ends after the Mechanical Hound stabs the pedestrian. In regards to Montag's feelings about Chicago, he is pleased that he finally remembers the city where he met Mildred, which is something that has been bothering him since the beginning of the novel.
In Part 3 of the book, Montag has escaped across the river. But the hunt for "him" keeps going on. Finally, it settles on a man that the authorities say is Montag. He has helicopter spotlights shining on him. The mechanical hound is released and it kills him.
The authorities need to find a scapegoat because they would look bad if they allowed someone who had done what Montag did to escape. As Bradbury says in the book, it "saves face" for the government to catch someone. As long as the public thinks it's Montag, everything is okay.
As for Chicago, I don't think he's happy about Chicago itself -- he's happy because he finally remembered where he and Millie met.