Mitchell Jarvis as Macheath, Natascia Diaz as Jenny and Erin Driscoll as Polly Peachum in The Signature Theatre’s production of “The Threepenny Opera” in Arlington, Va. (Marvin Joseph/The Washington Post)

For the real Brechtian deal, spend a few fulfilling minutes in the presence of Natascia Diaz, the sultry Jenny of Signature Theatre’s capable, lusty-voiced revival of “The Threepenny Opera,” as she sings of shark’s teeth and other pointed things pertaining to her ultra-dangerous lover, Mack the Knife.

With her hard/soft eyes — languorous glances suggesting both suffering and desire — Diaz inhabits the brooding underworld of Bertolt Brecht and Kurt Weill’s landmark musical with such a powerful sense of mystery you could spend the entire show trying to puzzle out what’s going through Jenny’s mind. Is it hate that drives this lady of the evening to betray the seductively corrupt Mack and send him to the gallows? Or is it the exact opposite?

Diaz’s pure embodiment of the enigma of Jenny gets in some crucial way at the essence of this sermonizing show that shames all of us who have and think too little of those who have not. It’s about brutal paradoxes, about redemption for the irredeemable, about devotion to the undeserving, about criminal justice serving the unjust and the poor dressing up to look poorer just so that the rich can get even richer.

The actress is pivotal to the most resonant moments of director Matthew Gardiner’s production, an updating of the 1928 musical that situates it in a venal, alienating, contemporary London. (This version, in a translation by Robert David MacDonald and Jeremy Sams, was unveiled at the Donmar Warehouse in the post-Thatcherite London of 1994.) And when it works best, this well-sung venture, with its fine eight-member band conducted by Gabriel Mangiante, successfully bottles that Brechtian sense of human progress headed in reverse, in the pursuit of all that’s sour and unholy.

It must be said, though, that this “Threepenny,” for all of its theater savvy and strong ensemble work, tends also to feel a little bit tame, and as a result, the musical can’t help but show its age. I’m not sure how exactly this can be avoided, for to paint Brecht’s parasites too grotesquely would be to turn “Threepenny” into a cartoon, as has happened in some past incarnations. In recent decades, the milieu of “Threepenny” has taken more striking form in musicals such as Stephen Sondheim and Hugh Wheeler’s “Sweeney Todd,” which wallows far more satisfyingly in the scurvy muck of London depravity. Even the parodistic “Urinetown,” by Mark Hollmann and Greg Kotis, conjured this world more zestily: Who can forget the succinct sendup of Brecht and Weill’s sardonic themes in “Urinetown’s” funny number, “It’s a Privilege to Pee”?

“Sweeney” and “Urinetown” are both known quantities to Signature regulars, and I would say that even if “Threepenny” feels a little past its prime, it’s a more than worthwhile evening in that vein, especially for those who have not seen it before. The hard-working Gardiner, at the helm for such recent, varied triumphs in Shirlington as “Dreamgirls” and “Really Really,” has cast his show with exceptional care: As the money-grubbing Peachums — whose business is controlling London’s licensed guild of beggars — Bobby Smith is just the right degree of unctuous, and Donna Migliaccio, cloaked by Frank Labovitz in the meticulous suits of a suave socialite, proves to be his match for scrupulous callousness.

As their daughter, Polly, Erin Driscoll effortlessly takes on and off the mask of guilelessness and gives Polly the earthy edge that lets us believe she can swim with the star-gangster Macheath and his school of piranhas. (She also does nicely by Polly’s big Act 1 numbers, “Pirate Jenny” and “Barbara’s Song.”) Rick Hammerly, meanwhile, pleasingly turns up the volume of “Threepenny’s” duality as Macheath’s former squeeze, Lucy Brown. As for Mack the Knife himself, Mitchell Jarvis, late of Studio Theatre’s “The Rocky Horror Show,” here offers up a persuasively shady bloke from the dark side who treasures the ladies even more than he does his freedom. Jarvis’s voice, which may be better honed for rock than for Weill, is nonetheless a sterling instrument for Macheath’s twisted musical profanation from the gibbet, “The Ballad in Which Macheath Begs All Men’s Forgiveness.”

The plot hangs so loosely about “The Threepenny Opera” that you feel the slightest nudge might send it all tumbling to the floor of Misha Kachman’s warehouse-like set, whose most colorful feature is a painting of the Union Jack. It’s posited here that, his father Prince Charles having renounced his claim, Prince William is ascending the English throne as Macheath’s reign of terror is finally coming to an end. Rather than lending the show an up-to-the-minute feel, however, the imagined current events draw further attention to the tale’s rickety quality. The modern moral tacked onto the evening, in which the actors beg us to remember the homeless, “as they’ve allowed us to make a play from their lives,” comes across as gratuitous rather than heartfelt.

When singing those moody Weill melodies, though, with the modernized lyrics Sams has added, this “Threepenny” beats with a plaintively compelling heart. And never more so than whenever Diaz makes an entrance.

The Threepenny Opera

Book and lyrics by Bertolt Brecht, music by Kurt Weill, with English translation by Robert David MacDonald and lyrics by Jeremy Sams. Directed and choreographed by Matthew Gardiner. Sets, Misha Kachman; music direction, Gabriel Mangiante; costumes, Frank Labovitz; lighting, Colin K. Bills; sound, Lane Elms, projections, Rocco DiSanti. With Paul Scanlan, Ryan Sellers, Jessica Thorne, Katherine Renee Turner, Thomas Adrian Simpson, Aaron Bliden, John Leslie Wolfe, Sean Fri, Jamie Eacker. About 2½ hours. Tickets, $47.30-$104.20. Through June 1 at Signature Theatre, 4200 Campbell Ave., Arlington. Visit or call 703-573-SEAT.