Midway through the crime drama American Gangster a man tells reputed drug lord Frank Lucas (Denzel Washington) that, “quitting while you’re ahead is not the same thing as quitting.”

In many respects, this is the most pivotal line in the film because it so perfectly sums up the fundamental force uniting both the narcotics officers and the drug smugglers they are supposed to be tracking.

The film tells the story of two men, Lucas, the real-life former drug kingpin, and Richie Roberts, narcotics officer who helped bring Lucas to justice. Both are on a crash course to discover the nature of their own general ethics within their chosen career paths. Neither can quit. There is too much at stake.

As the film opens, Lucas begins to take over his former boss Bumpy Johnson’s New York drug operation. Very little is done to stop the operation because the narcotics police are largely being paid off by Johnson and his associates.

Eventually, Lucas becomes so powerful, that he can arrive at publicized boxing matches, such as an Ali/Frazier fight, and sit in the second row.

Roberts, played by Russell Crowe, is a man dogged by an intense desire to live by a general code of conduct with respect to his law enforcement career. His ex-girlfriend is taking him to court to obtain sole custody of their son.

She argues that he is an absentee parent and cares less about his domestic life and more about proving he has ethics on the job, such as when he finds $1 million in unmarked cash in the trunk of a sedan and turns it all in.

Meanwhile, Lucas is building his drug empire. He travels to Thailand during the Vietnam War, purchasing his product directly from the source and having it shipped to the states in the coffins of returning dead soldiers.

For such an ethically reprehensible endeavor the film finds a way to brilliantly show the gray area that exists between the “good” cop Crowe and the “bad” kingpin Washington.

Lucas has a thirst for power, wealth and prestige. But he’s also portrayed as a charming, charismatic, church-going man who loves his mother and employees his family into the business when his “Blue Magic” heroin becomes the best selling drug on the streets.

Compared to Crowe’s character, Lucas is the model of stability and success, notwithstanding his chosen career path. Richie, on the other hand, is still dealing with his personal demons and wondering who he can trust while trying to bring down Lucas by any means necessary.

The “persistent-cop-takes-down-drug-kingpin” story line is nothing new to the cinema. What makes American Gangster, different and entertaining is the way it allows its characters to have depth beyond their chosen professions.

As played by Washington in a terrific performance, Lucas is a man who behaves as if he is as decent as he can be given the circumstances that dictate his success. He doesn’t necessarily want to kill anyone, but if that’s what’s needed to maintain his status, then he must consider it a viable option.

Crowe is also fine as the cop with something to prove. Josh Brolin is also a standout as the corrupt Det. Trupo, who does more to keep Lucas in business than Lucas’ own contacts overseas.

The script by Steve Zaillian, based on a short story by Mark Jacobson, is one to be savored. It cares more about the psychological and social mechanisms responsible for Lucas’ ascent to power than the “gold car and platinum rims lifestyle” that many other films glorify.

Director Ridley Scott gives us a crime tale that questions the ethics of all the characters, not just the ones peddling dope. And in doing so, it answers the question of why these complex characters cannot “quit while they are ahead.”