In Washington, D.C. today, the White House was taken over by North Korean terrorists. With the help of a rogue Secret Service agent, the President and his senior advisors have been taken hostage. The terrorists' leader, blaming the US for his parents' death during the Korean War, intends to obtain the launch codes for America's entire nuclear arsenal and detonate the weapons in their silos, obliterating the country.

Of course, this scenario is playing out not at the White House itself, but at the multiplex down the street from 1600 Pennsylvania Avenue. Where movie villains once sported thick Russian accents or exaggerated Middle Eastern features, today's entertainment antagonists reflect the world's growing concern over the erratic and impenetrable "Hermit Kingdom" of Northeast Asia.

And if the plot of the movie Olympus Has Fallen seems provocative, it's hardly more provocative than North Korea's actual actions of late-or more heartbreaking than the incidents of real terror witnessed this week on the streets of Boston.

In the past several months, North Korea's young and untested new leader, Kim Jong-Un, has annulled the 1953 armistice agreement that ended the Korean War - at least the sixth time now in the past two decades that North Korea has formally rejected the armistice. North Korea appears likely to test its medium-range Musudan missiles amid competing intelligence reports that its scientists may have developed a nuclear warhead small enough to place on such a missile.

It pulled out of the Kaesong Industrial Park (jointly-administered by the North and South), vowed to turn South Korea into "a sea of fire," and has taken aim at Washington, Los Angeles and Honolulu-even threatening to wipe Colorado Springs off the map.

It's against this backdrop that U.S. Secretary of State John Kerry embarked on his first Asian tour, reassuring allies in Seoul, Tokyo and Beijing. Despite this display of diplomatic solidarity-and a recent, more muscular demonstration of American bombers and F-22 fighter jets-Kerry's message was clear: the US has a pivotal role to play, but "China has an enormous ability to make a difference here."

Just a month after taking office, this is the first great leadership test for Chinese President Xi Jinping.

Though the U.S. has rarely exerted much pressure on the North Korean regime, China has remained North Korea's sole ally in the region. It is by far North Korea's largest trading partner, with trade volume between the two countries more than doubling from 2008 to 2011.

"Kim Jong-un's only constraints," Brookings Institute Senior Fellow Kongdan Oh observes, "are the fear that the Chinese might someday pull the plug on his economy, and the fear that his hard line military might turn against him."

While China feels some historic affinity for North Korea and considers the country a valuable buffer against the U.S. military presence in South Korea and Japan, it also fears a destabilizing influx of North Korean refugees should the regime fall. Even so, China's leadership has made only half-hearted attempts to influence North Korea's actions. Despite "crippling" Western sanctions, North Korean elites can be seen checking refrigerators and washing machines onto flights from Beijing to Pyongyang. Meanwhile, Kim's enormous financial assets-deposited in two Shanghai banks-remain unfrozen.

With each new aggressive act, however, Chinese support for its reckless, saber-rattling neighbor is wearing thin. Kim's latest nuclear test-just 60 miles from the Chinese border-infuriated and frightened the Chinese public, who've taken to calling North Korea's leader "Fatty Kim the Third" online. President Xi took the unusual step of chastising the Kim regime for "throwing a region and the world into chaos for selfish gain" and signed onto the latest round of UN sanctions.

Now, China must put aside Cold War paranoia and recognize that the best way to reassert control in its own backyard is by bringing North Korea back to the negotiating table. If China is truly an emerging great power, it should restart the decade-old Six-Party Talks between China, the U.S., Japan, Russia, North and South Korea. If Pyongyang resists, Xi must be willing to completely cut off North Korea's lifeline.

And what should the U.S. do?

First, the US shouldn't even consider relaxing our regional defenses. Our allies depend on us; and Japan and South Korea are rightly nervous about any breakdowns in the American nuclear umbrella.

Second, Washington should work with China to offer Kim a way out. Having blundered into a geopolitical game of chicken he's unequipped to win, experts suspect Kim is searching for a way to save face. The US should gladly provide him that - not through food aid of the sort that was so popular yet ineffective throughout Kim's father's similar bluffs in the 1990's, but by offering the assurance Pyongyang desperately seeks: that the US will not invade if the regime abandons its nuclear ambitions.

Third, if North Korea maintains its aggressive posture, the US should make clear it will bring a swift and disproportionate response. As STRATCOM commander Gen. C. Robert Kehler notes, we should make clear that North Korea "will not achieve their goals, and will pay an extraordinary price if they try." Or, in the unforgettable words of Sean Connery in The Untouchables, "He pulls a knife, you pull a gun. He sends one of yours to the hospital-you send one of his to the morgue! That's the Chicago Way."

Ultimately, Kim must choose between the Chicago Way and the Chinese Way. For its part, China must recognize, as the analyst Paul Haenle says, that "The continuing narrative that North Korea defies China, one of the North's only allies, at every turn...cuts across Beijing's goals of consolidated regional influence and eventual global great power status."

It's been 60 years since an uneasy truce brought an end to the shooting war on the Korean Peninsula. In that time, Olympus hasn't fallen-but China has risen. It's time for the world's largest country to act like it, and embrace its responsibilities on the global stage.

(The author is Founding Chairman of Business Executives for National Security, a nonpartisan organization based in Washington, DC. This is a personal comment.)