Meet Tristan (James Franco), an English knight picked to orchestrate the downfall of ironfisted Irish King Donnchadh (David O’Hara). Now meet Isolde (Sophia Myles), an Irish

There's no way to watch United 93 , Paul Greengrass' heartbreaking, pulse-pounding drama about the lone hijacked commercial airliner that failed to reach its target on Sept. 11, 2001, and not anticipate the dreadful outcome.

There's also no way to watch United 93 and not relive the surreal horror of the World Trade Center attacks and the jet that hit the Pentagon.

And there's no way to watch this extraordinarily powerful film and not be in awe of what human beings are capable of – both good and bad.

Already the subject of two TV movies and a shelf of books, the story of the 40 passengers and crew members aboard United Airlines Flight 93 from Newark, N.J., to San Francisco – and the four hijackers who seized the plane – could easily have been an exercise in exploitation, in jingoism. But Greengrass has couched United 93 in unwaveringly realistic terms.

With a screenplay based on interviews with government, military, and commercial aviation officials, on the report of the 9/11 Commission and on talks with the surviving family members of the passengers and crew, Greengrass delivers a wrenching chronicle of an everyday airplane ride that goes frighteningly awry.

Cast with unknown actors and, in several cases, with the real Federal Aviation Administration managers, air traffic controllers and military technicians who were working the morning of 9/11, trying to make sense of the missing radar blips and intercepted calls, United 93 is, in many ways, an educated guess of a movie.

The facts: Passengers telephone friends and loved ones, reporting in hushed tones that they've been hijacked; in turn, they are informed of the TV news flashes about two giant airliners rocketing into the twin towers. It is no great leap to conclude that their plane, and their hijackers, are on a similar mission.

The hypothesis: that a group of passengers, one of them a judo champion, and another a former athlete, decides to charge the terrorists and retake the cockpit.

United 93 takes that scenario and runs with it. Having cut back and forth between the plane and the airport towers, traffic control centers and North East Air Defense HQ on the ground – describing the communication lapses and panicky chaos that ensued – Greengrass keeps the last 30 minutes of the film in real time, inside the United jet.

Made with enormous respect to the real passengers (and their surviving friends and family), United 93 also manages to portray the four hijackers as something more than cutout Jihadist madmen. In one small but telling, and compelling, sequence, Greengrass intercuts shots of passengers reciting the Lord's Prayer with shots of the hijackers murmuring Islamic incantations.

It's Greengrass' way of asking a question that looms large in these post-9/11 days: Are we all praying to the same God, or is one man's God better than another, and one man's God vastly more terrifying?

Grade: A