In the first episode of I Know This Much Is True, Thomas Birdsey (Mark Ruffalo) asks his identical twin brother Dominick (also Mark Ruffalo) to read him some comforting words from the biblical book of Psalms. Much less devout than his brother, Dominick needs a little help finding it. "It's between the Book of Job and the Book of Proverbs," Thomas tells him. The significance of the moment becomes apparent before long. To get to the beauty of Psalms or the wisdom of Proverbs, Dominick's going to have to go through the suffering of Job. And though Dominick might feel like he's already being tested in that moment, as he rides along with his brother as Thomas is committed to a high-security mental hospital, he has no idea what trials await him.

Neither, at this point, do viewers of I Know This Much is True, at least those who haven't read Wally Lamb's 1998 novel of the same name. A best-selling Oprah's Book Club selection, the nearly 900-page novel resisted years of attempts to turn it into a film despite numerous offers. Ultimately, the rights reverted back to Lamb in 2014, who still held them as the current trend of turning dense novels into miniseries hit full swing thanks to projects like Big Little Lies and Sharp Objects. It's a case of good timing. The plot of I Know This Much Is True would need merciless trimming to fit to feature length. As a movie, it might also play as a merciless assault of misery. Here in HBO's six-episode miniseries, the misery has room to breathe.

The Best TV Shows and Movies To Watch While in Quarantine

It also benefits from a remarkable double performance from star Mark Ruffalo, who plays both Thomas and Dominick, twins in name and appearance but divergent in personality. Opening in 1990 against the backdrop of the build-up to the Gulf War, I Know This Much is True begins with its most jolting scene. Talking to himself in a public library, Thomas makes what he believes is a sacrifice to God to atone for the sins of the nation by cutting off his right hand. A paranoid schizophrenic who's taken a bad turn, Thomas resists doctors' attempts to reattach the hand and, after some deliberation, Dominick decides not to press the issue. He knows any effort to help can't overwhelm his brother's will, however much harm it might do him.

Unusually capable at depicting suppressed turmoil interrupted by explosions of emotion — there's a reason he made such a great Hulk — Ruffalo skillfully draws two distinct characters that still feel deeply connected, like different possible outcomes from the same turbulent background. On a technical level, it's an extraordinary accomplishment. Though identical, Thomas and Dominick have strikingly different facial features and physiques, a transformation accomplished by filming all of Ruffalo's scenes as Dominick first then shooting scenes without him while Ruffalo cut his hair, put on weight, and otherwise got into character to return and play Thomas. Some CGI effects using acting doubles factored into the illusion as well, but it's Ruffalo doing most of the work. His hair changes and his face puffs up across the two performances, but the real transformation comes from the way he carries himself and the way his eyes convey the different sorts of sadness each brother carries with him.

Mark Ruffalo and Mark Ruffalo, I Know This Much Is TrueMark Ruffalo and Mark Ruffalo, I Know This Much Is True

It's not a one-man show, however. Director Derek Cianfrance helps provide a sense of place that further fleshes out the world of the story. Set in the fictional eastern Connecticut town of Three Rivers, it captures the feeling of a place whose boom years faded with the changes of the '70s and '80s, furthering a sense of the weight of history felt by the characters. The industry that put it on the map has gone elsewhere, yet Three Rivers remains, unsure of what happens next. Cianfrance's feature films Blue Valentine (set partly in rural Pennsylvania) and The Place Beyond the Pines (set in upstate New York) established him as a director unusually good at capturing off-the-map Eastern places. (Long flashback scenes starring Italian actor Marcello Fonte as the brothers' grandfather bring the same skill to bear on the town's less-recent past.) Those films also established him as an actors' director, a reputation the series does little to dispel.

Jumping freely across the events of the Birdsey brothers' lives — and later, going back further into the family's origins — the miniseries slowly reveals their complicated, often tortured history, including the cancer death of their mother Concettina (Melissa Leo) three years prior to Thomas' shocking act. (Leo's only a few years older than Ruffalo but mostly plays Concettina in flashbacks.) As the brothers' abusive stepfather Ray, John Procaccino stays in the picture from beginning to end, an usually prominent role for an always reliable character actor. The identity of their biological father, on the other hand, remains a secret Concettina has apparently taken with her to the grave.

The Best New TV Shows of 2020

It's Thomas' self-mutilation that sets the events of I Know This Much is True into motion, but subsequent scenes reveal it as part of a larger chain of history, one tied to secrets buried in the past and attempts to forget more recent trauma that refuses to go away. As Dominick's ex-wife Dessa, Kathryn Hahn brings sensitivity and complexity to scenes that capture the tenderness that remains between two people who found they couldn't live with each other anymore. She's one standout among a cast of many, including Michael Greyeyes as an old schoolmate with whom the Birdseys have a fraught history, Phillip Ettinger as the younger Thomas and Dominick, a too-brief appearance from Juliette Lewis as a troubled academic, and Rosie O'Donnell in a terrific dramatic turn as a compassionate but clear-eyed social worker trying to steer both Thomas and Dominick out of the darkness.

It's that darkness that dominates the series and provides another reason I Know This Much Is True might work better as a miniseries than as a film: its intensity rarely lets up. Rob Huebel provides a few moments of comic relief as Dominick's friend whose acting ambitions keep crashing against his day job as a used-car salesman, but the bleakness can feel oppressive at times. That's appropriate to the material — and a good reason to watch this week-to-week as it airs on HBO rather than all at once — but the way it piles tragedy on top of mishap on top of calamity can be overwhelming at times (and this adaptation even cuts some of the misfortunes included in the book). As can Cianfrance's decision to lean into darkness; there's one shot that's pretty much the visual equivalent of "For sale: baby shoes, never worn." "How many families do you know that have so much f---ed up s--t happen to them?," one character asks in the final episode, but by that point the other episodes have already answered the question.

Kathryn Hahn and Mark Ruffalo, I Know This Much Is TrueKathryn Hahn and Mark Ruffalo, I Know This Much Is True

Still, it's a journey worth taking, and one that might not work nearly as well if it offered any distance from Dominick's troubles. Cianfrance takes an immersive approach that harmonizes well with Ruffalo's deeply felt performances. The space also allows for more complexity, particularly in Dominick's relationship with Ray, which forces Dominick to reckon with what happens when someone who mistreated him needs his compassion later in life, a realization that becomes part of a deeper understanding that suffering happens for a reason — even if it's just the reasons we impose on it after living through it.

TV Guide Rating: 4/5

I Know This Much Is True premieres Sunday, May 10 at 9/8c on HBO.