Frank McGuinness’s piercingly humane 1985 play Observe the Sons of Ulster Marching Towards the Somme begins in 1969 with an elderly Irishman’s tirade against God. One of 1400 members of the 36th Ulster Division’s 7000 soldiers who didn’t die by noon on the first day of the World War 1 bloodbath called the Battle of the Somme, he rails of that July 1, 1916, march to slaughter, " Answer me why we did it. Why did we let ourselves be led to extermination? " Then the ghosts appear, dark and mighty on a rise behind him, raising their blood-red hands, redolent of the provincial flag of Ulster, in salute. The rest of the play is a fugue-like flashback that illumines cranky old Kenneth Pyper’s Q&A with the Almighty. Dense with poetry, rhetoric, history, prejudice, terror, and compassion, it answers the bitter survivor’s rhetorical salvo with what Yeats might call a terrible beauty.

The red hand of Ulster, a thing of Irish legend, reaches through the play, from the 1969 prologue to the initial 1915 scene, which begins with a younger Pyper’s cutting his thumb while peeling an apple. " Blood, " he remarks with shattering irony, considering what is to come. " Hate the sight of it. " This scene depicts the first prickly encounter of the eight Ulster men who will share a makeshift barracks, pair off to wrestle with issues ranging from ancestry and sexuality to rant and religion, then bond in the trenches on their way to certain death. Shared prayers, a childlike hymn, and a horsing-around re-enactment of the Protestant victory at the Battle of the Boyne (which took place on roughly the same date, in 1690) are what they take with them into the doomed charge.

McGuinness, an Irish Catholic, switches sectarian sides for this still remarkably relevant meditation on masculinity and war, patriotism and jingoism, naked fear and human gallantry, that in the end uncovers the connection between fanaticism, on whatever side, and love. The self-loathing Pyper is the only one of the Ulster men who volunteers not for the conjoined honor of Empire and Ireland’s Loyalist Protestants but to commit suicide in uniform. He becomes an Orangeman not out of dedication to the Cause that has pumped up his fellow bits of cannon fodder but for love of these men.

Huntington Theatre Company artistic director Nicholas Martin had spent years wangling for the rights to Ulster (they had been withheld in hope of securing a major New York production of the work, which had been revived in Dublin in 1994 and by England’s Royal Shakespeare Company in 1996). He first staged the play on the Williamstown Theatre Festival’s tiny Nikos Stage last summer. The current production, a collaboration of the Huntington and Broadway in Boston (with eyes cast toward Broadway), unfolds on a grander scale but with most of the same actors, including Mulholland Drive’s Justin Theroux and Party of Five star Scott Wolf.

It’s hard to know what to make of Alexander Dodge’s almost whimsical set, its dominating element a lime-green parabola that stands in for both the hills of Ireland and the trenches of France. But Martin’s production captures both the ghostly pageantry and the feathered intimacies of the work. And Theroux, whose young Pyper grows from a preening, playful, disaffected cockiness to eloquent and emotional stewardship of the group, stands out in a field that includes Wolf’s touching and subtle portrait of a feisty young bully baker holding on to his nerve with white knuckles.

Observe the Sons is not a perfect work; it can seem fractured and schematic, even in its overriding magnificence. Most unconvincing is the character of Roulston, a lapsed Protestant preacher torn over whether being one of the " elect " makes him Jesus or just one of the guys. Still, Jeremy Shamos makes the seemingly schizoid fire-and-brimstone brooder human. Easier to fathom are big Belfast shipyard workers McIlwaine and Anderson, who are played with lumpen fervor by Jonathan Walker and Rod McLachlan. These two have a simple if brutish agenda that manifests itself in a two-man rabble-rousing Orangemen parade, complete with lambeg drum — but without any rabble.

Christopher Fitzgerald mixes boyish appeal with bitter insight as the irrepressible Crawford, the frank soldier (and half-Catholic) who’s never without a football, even at the gates of Hell. Dashiell Eaves brings a boyish vulnerability to softhearted Coleraine weaver Moore, who thinks he can’t endure but does, carrying with him Wolf’s seemingly dominant Millen. And Jason Butler Harner exudes both innocence and assurance as the lanky Enniskillen blacksmith Craig, Josie Hogan to Pyper’s ultimately transfigured Jamie Tyrone.

WHEN IT DEBUTED IN LONDON in 1986, Observe the Sons of Ulster Marching Towards the Somme won McGuinness the London Evening Standard’s Most Promising Playwright Award, and promise is what Jon Lipsky’s fiery but muddled Molly Maguire has, if you give greater weight to the better second act. Long-time local presence Lipsky has fine works to his credit, including Living in Exile, his streamlined version of the Iliad. This play, the first to be commissioned by Súgán Theatre Company, and presented here in its world premiere, is part docudrama, part human drama built on facts surrounding the 1860s-’70s Pennsylvania struggle between striking Irish coalminers and the mine owners and railway moguls who were out to break them. The secret, militant arm of the miners — 20 of whose members were hanged for crimes of violence — was called the Molly Maguires (though the existence of the Irish organization in Pennsylvania was never proved).

Lipsky’s play, with its cast of actual, composite, and imagined figures, focuses on one hotheaded, manipulated miner and his impoverished clan, so as to put a specific face on historical, highly political happenings. The result seems alternately recited and overwrought. And if you fail to bone up on these events by reading the materials posted in the lobby, the now intoning, now screaming first act, complete with bizarre rituals of slugging and poetry and a fiery scuffle between Irish strikers and German scabs, is hard to follow. The second has a tighter focus and uses the folk music woven into the piece to haunting effect. But with the exception of Jennie Israel’s miner’s wife, who’s feisty if stereotypical, the characters have little flesh on them.

The events of the play — underlaid by mostly mournful music, the plink of water dripping in the mines, and metaphors of suffocation — are based on fact. Jimmy Kelly, the central figure, is a composite of several arrested miner agitators who turned informant. And there are historical characters: " king of the Mollys " Jack Kehoe; Pinkerton detective James McParlan, who, posing as James McKenna, infiltrated the Mollys; and lawyer-turned-Reading-Railroad-president Franklin B. Gowan, who, astonishingly, was allowed to prosecute some of the Molly trials. Lipsky adds a family drama focused on Jimmy’s stormy relationship with his belittling but loving wife, Maura. She’s trying to put food on the table (snake is promised in one scene) while coping with the 1875 " Long Strike, " a dying miner father, and apprehension of the agitation in which her husband is secretly involved. When Jimmy blows up a pier and kills a policeman, McKenna, who has been romancing Maura’s sister, reveals himself as a Pinkerton and turns the hapless killer in.

In the tighter second act, Gowan frightens Jimmy into turning state’s evidence. Kehoe, needing " more time to make more trouble, " prevails on Maura to testify that her husband is telling lies. (Even this development is based on fact: the wife of one informer called him a liar, traitor, and " dirty little rat " from the stand, then reconciled with him after the trial.) Whereupon Gowan, not one to let legal no-nos like witness intimidation stand in his way, tries to scare Maura into skedaddling home.

Gowan is portrayed in Molly Maguire as a fancy-talking, cross-bearing villain in a commedia dell’arte mask, but Victor Warren, who doubles as McKenna, plays him with a flourish, and the war of words between Gowan and Israel’s shaken but untoppled Maura is the sparkiest part of the play. The reliable Billy Meleady brings a tough but never bellicose fervor to Kehoe, and Stacy Rock contributes sly charm and a pretty singing voice to Maura’s sister, Maryann. But Derry Woodhouse plays Jimmy on two notes: seething and hysterical.

Lipsky and director Carmel O’Reilly have tried to do some interesting things with Molly Maguire, staging it in dimness to suggest the oppressiveness of the mines, with the seven-actor company slipping out of their characters to stand in for miming miners and deliver grim narration and urgent scraps of song. (The Brechtian " Betrayal Song " is among the show’s more effective moments.) But the first act veers between wooden and chaotic, and even the better second seems more a history project than a play.