This is one of my favorite movies. Denzel's character Alonzo is a complex mix that catches you in twists and turns and you can't decide if you like him or hate him. Ethan's character Hoyt feels like he could be you or me on the first day of a job and all that entails.
I'm not going to give away the plot, but it focuses on a young police officer trying to work his way up to Detective by joining an elite Narcotics Division ran by a tough, street-wise lieutenant. He's trying to go out of his way to impress his new boss who isn't going to make it easy for him.
It's a great movie, I don't want to give you any more than that. Highly recommended.