A retired Chicago cop. A folder he shouldn't open. A confession that could burn down the city.At 4:15 on a freezing January morning, a young man in an Audi slips a bag of cash into the depository slot of a Ukrainian Catholic church and drives off into the dark. It's the kind of thing nobody notices. Except two cops notice everything.Pat Conlon and Carlos Martinez have worked Chicago's streets together for decades — partners, brothers, throwbacks who still believe in the job...