Starring Gerard McSorley. Rated PG. Opens Friday, March 24, at the Fifth Avenue Cinemas

If all of the thousands of nationalist bombs that exploded in Northern Ireland between 1969 and 1999 had been murderous in intent, the population of Erin's northernmost counties would doubtless have shrunk to something like Iceland or Malta's.

Nevertheless, the fact that almost all of the IRA's relatively few willfully homicidal explosions were directed against either British security forces or civilian targets in England did not prevent hundreds of innocent Ulstermen from winding up in the morgue, while thousands of others got sent to the emergency ward, many to emerge in a permanently disabled state. Even when telephone warnings were given, the time allotted was rarely long enough to save everyone, and some horrendous screwups inevitably occurred.

Of all these high-explosive tragedies, the one at Omagh was by far the worst. The bomb that detonated on August 15, 1998, killed 29 people and injured more than 300, making it the worst atrocity in the latest round of Ireland's perennial "Troubles". An aggravating factor was the splinter Real IRA's decision to cut the usual one-hour warning time in half and to seriously garble the warning that it did deliver, resulting in police actually steering people toward the explosion.

Omagh is the real-life story of one man (Michael Gallagher, played by Gerard McSorley) who tries to make sense of the death of his grown son.

To deal with his grief, he forms an organization made up of the victims' relatives and seeks justice for the irreparable wrongs they have suffered. Despite a supposedly changed political climate, progress proves to be painfully slow.

Nevertheless, Gallagher persists in his demands for redress, and his organization remains on the trail of the bombers to this very day, with a civil suit against five defendants on the horizon.

Pete Travis's naturalistic direction is believable to an almost documentary degree, and the dialogue by coproducer-cowriter Paul Greengrass (the man who made Bloody Sunday, a 2002 film about a rather different Northern Irish atrocity) never hits a false note.

Ultimately, however, this intensely moving film belongs to McSorley (who is as sympathetic here as he was dislikable in Bloody Sunday), the quiet, unassuming Irish Gandhi who does not distinguish between Protestant and Catholic blood loss. The actor spent a lot of time with the real Michael Gallagher, who was subsequently astonished at how exact McSorley's impersonation proved to be.

Omagh is one of the best films of the year, as well as one of the most important. Don't miss it.