IT IS a musical jinx, in many ways worse than "A Whiter Shade of Pale." Melodically monotonous, fantastically ill omened, "Amazing Grace" is as essential to disasters as makeshift shrines with teddy bears and Mylar balloons. And the hymn has been a key to the success of depressing movies for decades. If you hear an a cappella version on a soundtrack, you can judge that the audience really got hit with it. Still, "Amazing Grace" is utterly democratic. It sounds neither better nor worse performed by an operatic soprano or a band of kilted Scotsmen with bagpipes, and the latter is the performance that closes the film Amazing Grace, perhaps in honor of an especially strange novelty hit of the late 1960s, the last time that bagpipes made the Top 40. We learn from the film that the dirge was composed by a sackclothed penitent, half-mad from remorse. Ah, but was it the guilt that unhinged him or the song itself? Amazing Grace uses the song's history to hold together a rambling biopic. Its era is the turn of the 1800s. Its subject is the William Wilberforce (Ioan Gruffudd, never better), the MP who devoted his frail health to stamping out the British slave trade. Stricken with stomach troubles and opium addiction, Wilberforce was still an activist's activist.

Director Michael Apted assures us that very socially unsuitable people always make reform. And there are parallels between the distant struggles and our own. Amazing Grace notes that some consumers of the day did what they could by boycotting slave-made sugar. Yet the scenes of flower-child transcendentalists—Wilberforce wriggling in a pasture, staring at the clouds—are a heavy cross for the mean to bear. "I, find God? ... I think he found me," says Wilberforce. Such was the Romantic Era; the rise of the individual marked by moments that are still embarrassing 200 years later.

These cringe-inducing moments—William's courtship with Barbara Spooner (Romola Garai) also delivers some—never seriously interfere with the progress of a richly staged, engrossing film about a well-spoken, politically complex era. The casting is happy throughout. The estimable Bill Paterson plays a Scots MP with some money in the slave trade; Ciaran Hinds is a dour Tory ringleader; Toby Jones turns up the decadent-looking, wizened Duke of Clarence. And Rufus Sewell plays Thomas Clarkson, one of those political hotheads every more moderate activist has to have behind them.

Apted doesn't have to explain the character of the minister Charles Fox; he lets Michael Gambon's molting periwig and air of sated slumber do it all. Best of all is Albert Finney as John Newton, the composer of "Amazing Grace." Newton was a former slave-ship captain who lived like a hermit in penitence. In a few spare scenes, Finney's theatrical precision and vast rumbling voice turn the role of Newton into a study for King Lear. When it comes time to tell of the way Africa was chained and raped, Apted trusts the gentleness of the audience. He gives us the horror, as Shakespeare would have. Rather than looking into it, we look into its reflection, into the stricken face of a shamed man whose misery is still audible in the tragic notes of that gloomy song.

Amazing Grace (PG; 111 min.), directed by Michael Apted, written by Steven Knight, photographed by Remi Adefarasin and starring Albert Finney and Ioan Gruffudd, opens Feb. 23 at Century Capitol 16, Oakridge 20, Mountain View 16.

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