I Know This Much Is True Season 1 - The Heart of the Story - Mark Ruffalo - featurette - Plot synopsis: Based on the 1998 bestselling novel by Wally Lamb, adapted and directed by Derek Cianfrance, this limited series follows the parallel lives of identical twin brothers, played by Mark Ruffalo. A family saga, it tells a story of betrayal, sacrifice, and forgiveness set against the backdrop of 20th-century America.