To prevent this, the U.S. has pinned its hopes on Saad Hariri, a businessman’s son with little political know-how. Saad came to power as head of the Future Movement party in 2005, after assassins killed his father, Rafik Hariri, the nation’s former prime minister and a critic of Syria, in a Valentine’s Day bomb blast. The explosion cratered a city street and left 23 people dead. It so outraged the nation, which blamed Syria, that a populist uprising quickly forced Syrian troops to withdraw. Then, in one of the most stage-­managed revolutions ever to play out on TV screens (midwifed by local advertising execs and spin-doctored by U.S. diplomats, who coined the term Cedar Revolution to sell it to Americans who might find its real name, Independence Intifada, off-putting), Saad rode his father’s funeral procession into office. He now holds his father’s old parliamentary seat and effectively controls the sectarian government through his majority party. This fall, if all goes as planned, he could be chosen as Lebanon’s second-youngest prime minister ever.

It is not a job he wanted. Saad Hariri had been living a rewarding life in Riyadh, Saudi Arabia, running the family’s $8 billion construction, banking, and telecom group, Saudi Oger. The Hariris are one of the wealthiest families in the Middle East, if not the wealthiest non-oil clan. They are part owners of the $37.5 billion Arab Bank, one of the largest financial institutions in the region. Their construction arm, second only to the bin Ladens’, is taking part in a $1.5 billion rebuilding project in downtown Amman, Jordan. Their purchase of Türk Telekom last year for $6.55 billion, spearheaded by Saad, was the biggest private deal in Turkey’s history.

Along the way, the family has also laid claim to some strategic trophy properties, including the 75-story Texas Commerce Tower (now known as the J.P. Morgan Chase Tower) in Houston. Rafik’s name adorns the School of Management building at Boston University, where his eldest son, Bahaa, attended college and now sits on the dean’s advisory council. When Rafik died at the age of 60, he was among the richest politicians on the planet. The fortune he left behind made three of his children the world’s youngest billionaires.

Yet despite their vast wealth and investments across several continents, no real estate is more valuable—or more meaningful—to the Hariris than Lebanon itself. There is loyalty to the homeland, to be sure, as well as Rafik’s legacy. But there is also the $2.5 billion of the nation’s debt the Hariri bank holds (debt Rafik helped run up as prime minister). And there are billions more in development projects, including an $18 billion downtown Beirut rebuilding effort, which could be in jeopardy should Hez­bollah seize power. With its patriarch gone, the family empire is at risk. Without a strong hand to guide Lebanon, the country itself is at risk.

This past year has been the ­bloodiest and most destabilizing for Lebanon since the fratricidal civil war from 1975 to 1990. Yet despite the car bombs, the shootings, and the attacks on United Nations peacekeepers that have beset the country all summer, the coming weeks could pose the darkest challenge to Saad Hariri and his U.S. patrons. On September 25, Lebanon’s parliament is scheduled to elect a replacement for the current Syrian-backed president, Émile Lahoud, a man who openly despised Rafik Hariri and whom Saad considers an accomplice in his father’s death. Political experts expect the Future ­Movement-dominated parliament to elect one of its own to the presidency. With Lahoud out of the way, Western officials expect Saad’s party to choose him as the next prime minister, giving him political stewardship of the entire government. Lahoud, however, has other plans.

In a veiled political threat, Lahoud has suggested he may form a par­allel government. The result could be a constitutional meltdown, if not civil war. The potential fallout is made more perilous by a U.N. report that new weapons are flowing across the Syrian border into the hands of Hezbollah, as well as to Islamic militants living in the country’s Palestinian refugee camps, whom the army has been battling since May in the deadliest challenge to the country since the civil war.

This means that Saad is under great pressure to deliver. The pressure is coming not just from the White House but from his own family. Saad must succeed amid rumors that his stepmother, Nazek—who holds court in a gilded Paris mansion that once belonged to Gustave Eiffel and heads the family’s powerful charity foundation—is not happy with his handling of the crisis. “She herself has political ambitions,” says a Western official. Saad must succeed as his older brother, Bahaa, a 41-year-old financier, expresses his own political ambitions in the Lebanese press. But most crucially, Saad must succeed under constant threat to his own life.

Since his father died, bombs or bullets have claimed the lives of seven of Saad’s anti-Syrian political allies. The murders are part of a deadly chess game; with each parliamentarian killed, Saad comes closer to losing his majority control. (Five more dead and it’s over for his group.) The most attractive targets are members of the Hariri-controlled cabinet. Almost two weeks before we first meet, on the eve of last December’s demonstrations, Saad’s closest friend, Pierre Gemayel, a 34-year-old cabinet minister who was expected to become the next president, was gunned down on a Beirut street in broad daylight. In this macabre standoff, Saad’s death could lead to a dire endgame and turn Lebanon into a black hole of conflict.

“This was not a choice,” Saad tells me, gesturing to the darkened windows, the advisers who reek of cigarette smoke, and beyond to the guards brandishing assault rifles in the street, protecting the entrance to his refuge. He tears the Velcro off his splint, flexing his swollen fingers. Then, just as gingerly, he wraps it back in place. “One has no choice in such situations,” he goes on. “The call that we had, as a family, we just had to do it. It’s a burden, a responsibility.” When I ask what happened to his hand, he reveals a streak of dark humor. “When Pierre died,” he says, studying the hand for a moment, then looking up with a smirk, “I punched a door.”

It’s not easy to get into Koreitem or to gain an audience with Saad Hariri. He rarely grants interviews. Unlike his father, who built a media empire of radio and TV stations and newspapers, and cultivated journalists and enjoyed their gossip at local cafés, Saad prefers to issue statements. And when he does, it’s usually in front of a nest of cameras feeding to the family-owned Future TV network. And it’s usual to vent at Syria.