Steve is an NYPD detective and Tony is a defense attorney, and both of them are very good at their jobs. At first Steve doesn't really like Tony, because he thinks that he's just helping criminals get away with their crimes for the sake of money, and the two of them generally don't get along. Then Steve gets framed for a murder, and for some reason beyond his comprehension, Tony takes his case pro bono.

(Bonus if as Steve and Tony eventually get to know each other better, Steve learns that Tony only takes a client on if he truly believes they're innocent.)