Plot Synopsis

Based on Wally Lamb's book of the same name, I KNOW THIS MUCH IS TRUE is a six-part limited drama series starring Mark Ruffalo, who also serves as an executive producer, as identical twin brothers Dominick and Thomas Birdsey in a family saga that follows their parallel lives in an epic story of betrayal, sacrifice and forgiveness. The series shows Dominick and Thomas at different stages in their lives, beginning in their present with both brothers approaching middle-age, filled in with Dominick's flashbacks to their young adulthood.

Melissa Leo stars as Ma (Concettina Ipolita Tempesta Birdsey), mother of Dominick and Thomas; Rosie O'Donnell as Lisa Sheffer, a social worker for unit two at the Hatch Forensic Institute; Archie Panjabi as Dr. Patel, Thomas' newly appointed psychologist; Imogen Poots as Joy Hanks, Dominick's live-in girlfriend; John Procaccino as Ray Birdsey, Dominick and Thomas' stepfather; Rob Huebel as Leo, Dominick's best friend; Philip Ettinger as the young adult Dominick and Thomas Birdsey; Aisling Franciosi as young Dessa Constantine; Michael Greyeyes as Ralph Drinkwater, a former classmate from Dominick and Thomas' youth whose life intersects once again with Dominick; Guillermo Diaz as Sergeant Mercado; Marcello Fonte as Domenico Onofrio Tempesta, Dominick and Thomas' maternal grandfather from Sicily; Bruce Greenwood as Dr. Hume, head of the board at the Hatch Forensic Institute; Brian Goodman as Al, an older cop; with Juliette Lewis as Nedra Frank, a self-absorbed grad student hired by Dominick; and Kathryn Hahn as Dessa Constantine, Dominick's ex-wife.

Episode 1 (Sunday, May 10, 2020 at 9pm): After paranoid schizophrenic Thomas Birdsey has a violent public breakdown, Dominick Birdsey finds himself stepping up to defend his identical twin brother in unexpected ways. As he navigates the fallout of Thomas' actions, Dominick reflects on their childhood growing up under the tyrannical rule of their volatile step-father, Ray, and their persistent desire to know the identity of their biological father. Dominick crosses paths with the prickly Nedra Frank as he attempts to have his grandfather's manuscript translated from Italian into English as a gift for his ailing mother. Written for television by Derek Cianfrance; directed by Derek Cianfrance.

Episode 2 (Sunday, May 17, 2020 at 9pm): Tensions rise between Dominick and his live-in girlfriend, Joy, as the media begins to take an interest in Thomas' case. In his attempt to have Thomas released from the Hatch forensic institute for the criminally insane, Dominick finds a potential ally in social worker Lisa Sheffer, but learns that helping his brother may be more difficult than he thought. Dominick clashes with Thomas' new psychiatrist, Dr. Patel, as she begins to probe into his past. We learn about the shocking tragedy that triggered the dissolution of Dominick's marriage to Dessa. Written for television by Derek Cianfrance; directed by Derek Cianfrance.

Episode 3 (Sunday, May 24, 2020 at 9pm): Sheffer preps Dominick for a pivotal hearing with Hatch's review board that could decide Thomas' fate. A chance encounter with an old classmate brings painful childhood memories to the surface. Dominick reflects on his and Thomas' time together at college, during which he met Dessa and the signs of his brother's illness first began to manifest. Joy attempts to remedy the problems in her and Dominick's relationship. Written for television by Derek Cianfrance; directed by Derek Cianfrance.

Episode 4 (Sunday, May 31, 2020 at 9pm): Despite the protestations of those closest to him, Dominick returns to work before fully recovering from his accident. Heavily medicated, Dominick recalls the disturbing incident that lead to Thomas' first hospitalization while counting down the hours to Thomas' hearing with the Hatch review board. Written for television by Derek Cianfrance; directed by Derek Cianfrance.

Episode 5 (Sunday, June 7, 2020 at 9pm): Upon learning the details of his Sicilian grandfather's arrival in the early 1900s to Three Rivers, Dominick becomes convinced his family is cursed -- a conclusion that Dr. Patel pushes back against. A startling update on Thomas from an unlikely source prompts Dominick to take drastic action.

Episode 6 (series finale; Sunday, June 14, 2020 from 9-10:20pm): A lifetime of animosity between Dominick and Ray spills over in public at an inopportune time. After an unexpected tragedy, Dominick seeks reconciliation with those he has hurt. The question that has plagued Dominick all his life is finally answered.