Michael Apted's well-intentioned yet often pedantic "Amazing Grace" is a good — and important — story, not always well told. It's a fact-based, historical drama about a hero whose name many of us may not know: William Wilberforce, the British politician who fought tirelessly to end the slave trade in the late 18th and early 19th centuries.

A close friend of the young prime minister, William Pitt, Wilberforce joined Parliament in his early 20s and devoted his life to the abolitionist movement and, later, to the emancipation of slaves. He died in 1833 at 73, three days after the Abolition of Slavery Bill was passed in the House of Commons. Wilberforce's epitaph, in Westminster Abbey, notes that while he was "a leader in every work of charity," his name will forever be identified with "those exertions which, by the blessing of God, removed from England the guilt of the African slave trade, and prepared the way for the abolition of slavery in every colony of the empire."

His was an inspirational life, and Apted's film, scripted by Steven Knight, sometimes vividly captures that passion. Played energetically by the Welsh actor Ioan Gruffudd, Wilberforce's youth and determination has a spark in the early scenes, as the young politician begins to realize that perhaps he can make change. As Pitt (Benedict Cumberbatch) observes, "We're too young to realize that things are impossible."

And Apted has cast his film well, with memorable turns from Romola Garai as Wilberforce's wife, Barbara (Garai is throaty-voiced and mature here, worlds away from her sweetly girlish work in "I Capture the Castle" and "Vanity Fair"), Michael Gambon as the imperiously witty M.P. Lord Fox, a wild-haired Rufus Sewell as Wilberforce's ally Thomas Clarkson and a fragile-looking Albert Finney as pastor John Newton, a former captain of a slave ship, who wrote the words to the hymn that gives the movie its name.

But the problem here is in whittling an epic tale down to less than two hours. Knight's screenplay too often resorts to awkward exposition to get the details out, and Apted has a tendency to let soaring, too-noble music (by David Arnold) overcome the subtlety of the actors' work. And the intriguing character of Oloudah Equiano (played by musician Youssou N'Dour), a former slave turned writer and abolitionist, is given short shrift. His big moment on camera is an awkward close-up, featuring an all-too-perfect tear trickling from his eye.

Despite its flaws, "Amazing Grace" works admirably as a history lesson, and audience members will surely leave wishing to know more about Wilberforce's life and times. By that measure, the film is a success; you just wish this tribute were more artful. Apted has shown, in films like "Coal Miner's Daughter" and the "Up" documentaries, that he can be an effortless storyteller; here, unfortunately, the effort shows too clearly.

Moira Macdonald: 206-464-2725 or mmacdonald@seattletimes.com