A single performer’s double act is among the showier maneuvers that can be attempted on film. There’s the technical aspect: Getting one actor, twice, into the same frame — or cutting to fool the mind into thinking that’s so — is inevitably showy. (When David Fincher cast one Armie Hammer to play two Winklevoss twins in “The Social Network,” it felt, more than anything, like an attempt to show off all the director could do.) And, too, there’s the way it maximizes the performer, giving opportunities for more acting as — from Nicolas Cage in “Adaptation” to James Franco in “The Deuce” to, yes, Lindsay Lohan in “The Parent Trap,” performers amp up the differences in their dual portrayals. All those actors capitalized, hugely, on the chance to create divergent characters who shared every physical detail, but little more.

Mark Ruffalo’s work in the limited series “I Know This Much Is True” continues in that tradition, but less through explosive showmanship than a more minor-key sort of skillfulness. Ruffalo, playing twins Dominick and Thomas Birdsey, is given ample raw material: The script, based on Wally Lamb’s novel, places Dominick, a relatively even-keeled fellow, in perpetual counterpoint to Thomas, whom we first meet when he cuts off his own hand in a public library. It’s an act of ritual sacrifice that Thomas believes will end the then-ongoing first Gulf War, and it’s also a way for the viewer to distinguish between two brothers, who now only have three hands between them. But when we see Dominick by Thomas’ bedside in the hospital, commonalities emerge. Dominick, acceding to Thomas’ request that doctors not attempt to reattach the severed hand, bears an attitude of irredeemable sadness that seems to share a border with Thomas’ ecstatic brokenness. Both brothers carry the weight of the world; Ruffalo, playing off himself, illuminates how they shoulder it differently even as he reveals the simple fact that the burden is indeed shared.

Ruffalo’s performances carry the series. This is his two-man show, with supporting characters glimmering in and out. In the main action, Dominick is providing care to Thomas, a brother who has for his entire life represented both a responsibility and a very rare source of mutual support, however conditional. Dominick is also recalling their entire story: Transported by memory, he examines the collapse of his marriage (with his ex-wife, Dessa, played by Kathryn Hahn, wrenching and mordant as ever) following the sudden death of their daughter. He further delves into the history of their family, from recent times, with a mother (Melissa Leo) ill from and eventually felled by cancer, to the farther-flung. Dominick hires a translator (Juliette Lewis) to interpret his grandfather’s handwritten memoir and, in so doing, finds out about the recurrence of twins throughout his ancestral line.

In moments like these, one senses that the attentions the show places away from Ruffalo’s characters, however limited, still end up misspent. We get, for instance, significantly less of Leo’s character than we do of Dominick’s grandfather, seen speaking subtitled Italian in flashback. It’s arguable that the absence of the twins’ mother is as impactful as was her presence, but the practical effect is to keep us away from a deeper understanding of precisely what is going on. As if operating according to the mental rhythms of someone unable to cope with grievous loss, the show skitters about, showing, for instance, a lengthy scene of Dominick and Thomas as young boys on an unpleasant but unremarkable school field trip while alluding, elsewhere, to grievous abuse that we see only fleetingly.

The show may, perhaps, be too effective for its own good at inhabiting Dominick’s mind. In its here-there-and-everywhere approach to the incidents of his life, it mirrors the thoughts of a person panicked by a situation coming to a head. But audiences could be forgiven, especially watching episodes on a weekly basis, for wondering what it all adds up to. A reveal late in the run purports to be the solution to a mystery the viewer may not have known was even pertinent; the throughlines of various relationships are frayed, and we’re meant to deduce via performance the ties of love and pain between, say, Dominick and Dessa.

Which is not to say that the performances don’t get us most of the way there! Hahn, for instance, furthers the case that she’s one of the very top actors of the current era of TV with a portrayal that glints with things she can’t or won’t say, if only because she’s too weary. Dominick, meeting Dessa for the first time in a long while, tells her that he sees a certain irony: “It’s funny, people used to predict that you and I would be the ones who stuck it out.” Her flat “It’s funny,” cautiously ironed out of all emotion, says as much as any entire scene the two share.

Derek Cianfrance, who wrote and directed every episode, is no stranger to the territory he walks here, that of unremitting sadness as lived through characters to whom we’ve grown painfully close. In “Blue Valentine,” his 2010 breakthrough feature, we experience a festering romance, and then a breakup, via performances (by Ryan Gosling and Michelle Williams) witnessed with an almost unbearable intimacy. And in 2013, Gosling’s death at the end of the first act of Cianfrance’s “The Place Beyond the Pines” hits like a wallop, arriving as it does after the audience has come to feel his ambitions and his weaknesses with something more than sympathy.

This kind of anguish wears more easily at the length of two-ish hours and a single sitting than it does over six weeks’ worth of hourlong episodes. What progress is made in Dominick’s and Thomas’ stories tends to be fitful, wrenched forward through painstaking personal work but to little apparent result beyond forcing us to feel more and more pain. Therapy sessions, for instance, with a character played by Archie Panjabi, or debriefs with a social worker played by Rosie O’Donnell, less advance what plot there is than continue the eddying motion of Dominick deeper into despair. That Thomas’ tenuous grasp on reality has brought him great pain is clear; that Dominick sees his own situation all too clearly yields much the same result. Ruffalo illuminates both states beautifully but that doesn’t quite remedy the fact the show does little to illuminate anything beyond the two men’s immediate circumstance.

There are elements to recommend “I Know This Much Is True”: Down the line, the supporting performances are shot through with soulfulness and a sort of stern determination that is a comfort. (O’Donnell is particularly fine, in a take-no-guff role that demonstrates her facility for transmitting humanity even, or especially, through gruffness.) And, set in rural Connecticut, the series easily slots into a sort of New England melodrama — think “Manchester by the Sea” or, on the wilder end, “Shutter Island” — in which grief is, ultimately, to be borne. There’s less a lesson there than a sort of more-relatable-than-ever stoicism.

But in the end, “I Know This Much Is True” cannot fully bridge a credibility gap. Dominick has suffered more extravagantly than can reasonably be imagined, and at a certain point, we cannot help shutting down a bit — in part for the extremity of the agony, and in part because it leads nowhere. That the show’s final moments feel random perhaps cannot have been avoided: Where does one go from the depths to which this story has plummeted?

Through it all, Ruffalo is his own best supporting actor — he proves, doubly, why Dominick keeps going, by illuminating the love that Dominick has for Thomas and that which Thomas, sustaining them both, reciprocates. Ruffalo’s the one you’ll watch for. But with all the talent Cianfrance brings to a show that’s ultimately a mismatch for his gifts, “I Know This Much Is True” ends up being precisely the sum of Ruffalo’s two parts.

‘I Know This Much Is True’ Starring Mark Ruffalo: TV Review

HBO. Six episodes (all screened for review).

  • Production: Executive producers: Derek Cianfrance, Mark Ruffalo, Gregg Fienberg, Lynette Howell Taylor, Ben Browning, Glen Basner, Anya Epstein and Wally Lamb
  • Cast: Mark Ruffalo, Melissa Leo, Rosie O’Donnell , Archie Panjabi, Imogen Poots, John Procaccino, Rob Huebel, Philip Ettinger, Aisling Franciosi, Michael Greyeyes, Guillermo Diaz, Marcello Fonte, Bruce Greenwood, Brian Goodman, Juliette Lewis, Kathryn Hahn