August Wilson’s “Gem of the Ocean” is a mountain of a play, epic from the opening seconds when a character named Citizen storms into a 1904 Pittsburgh kitchen desperate to see an oracular woman who is 285 years old. In the chronology of Wilson’s cycle of plays sweeping through the 20th century of black American life, “Gem” sits at the beginning while taking a heavy account of the past.

That’s a lot to live up to, and this new production at Round House Theatre is often — though not quite always — up for the hike. The chief pleasure is the crackling chemistry between the frantic young Citizen (played by Justin Weaks) and the sage elder, Aunt Ester (Stephanie Berry). As Citizen, an earnest young man from Alabama already at sea in the North, Weaks is shaken to his core; you can hear it in his quavering voice, see it in his rigid body. Berry’s Ester, on the other hand, is cool as can be. Ester knows the whole story, and Berry acts the role naturally, letting mystical authority bloom from her character’s knowledge, rather than from any ornate supernatural style.

That earthy, everyday tenor typifies the cast’s approach under director Timothy Douglas: The actors play these flesh-and-blood people without laboring to make a masterpiece sing. But don’t be fooled. Wilson, writing near the end of his life, created a near-operatic drama infused with long speeches — confessions, testimonies and even sermons, really, on history, on freedom and justice, and on the terribly elusive quality of inner peace, which the jittery Citizen sorely lacks. Wilson’s plot hinges on a simple bucket of nails stolen from a mill, yet it climaxes in the slave trade’s brutal ocean crossings as Ester conjures something she calls the “city of bones.” In telling all this, Douglas’s actors are familiar and grounded, but they are emotionally coiled all night. The pace of their speech never slacks, and the tension seldom backs off.

The spell cracks now and then, though, as the cast of seven performs on designer Tony Cisek’s wooden raft of a rustic kitchen-dining area in a house the occupants call “sanctuary.” It’s moored by small boardwalks leading offstage left and right, and backed by a tall staircase and looming wall. Veteran viewers of “Gem” — and there will be plenty, for Wilson remains one of American theater’s staples — will wait for this design’s secrets to be revealed, and the show does indeed pack an incandescent surprise in the second act. That the design is more expressive than the actors’ bodies in that instant is one of the snags that keep this “Gem” in the category of very good, but not flawless.

So, too, are speeches that can grow brittle at top volume, though for the most part Wilson’s figures are embodied with brisk confidence. The complexity of the characters pops out: Alfred Wilson is amiable yet dangerous as Solly Two Kings, a collector of dog waste (playwright Wilson had his reasons) who shares a formidable Underground Railroad past with Eli (Jefferson A. Russell, stolid as the household’s sentry).

Wilson’s poetic approach to character gets especially florid with Caesar, the ironically named lawman played with a boxer’s snarl and stance by KenYatta Rogers. Caesar is the melodrama’s villain, yet when he enters, Wilson lets him talk and talk and talk, with the pugnacious Rogers delivering the lines like blows until you understand this man’s tangled journey and tortured notion of justice. Punchlines are rare, so when Stori Ayers, as Ester’s serious housekeeper-cook, Black Mary, finds a laugh with Berry’s Ester, the comic relief is grand.

Wilson has been such a perpetual presence on stages for decades now that it’s easy to forget how many people haven’t been introduced to this singularly deep body of work. The “Gem” on display at Round House — the final offering before the company closes its Bethesda home in January for renovations and returns next fall, performing two shows in the meantime on the Shakespeare Theatre Company’s Lansburgh stage — gets the scale of the ambition and the blunt facts of its people. And in the archetypal mother-child bond that evolves out of the fable between Berry’s calm Ester and Weaks’s journeying Citizen, the show finds its soul.

Gem of the Ocean, by August Wilson. Directed by Timothy Douglas. Lights, Andrew Cissna; costumes, Kara Harmon; sound design, Justin Ellington; music director, Darius Smith. With Michael Glenn. About 2 hours 45 minutes. Through Dec. 23 at Round House Theatre, 4545 East-West Hwy., Bethesda. $30-$82. 240-644-1100 or