Thirty-something Captain Sam Cahill and his younger brother Tommy Cahill are polar opposites. A Marine about to embark on his fourth tour of duty, Sam is a steadfast family man married to his high school sweetheart, the aptly named Grace, with whom he has two young daughters. Tommy, his charismatic younger brother, is a drifter just out of jail who's always gotten by on wit and charm. He slides easily into his role as family provocateur on his first night out of prison at Sam's farewell dinner with their parents, Elsie and Hank Cahill, a retired Marine. Shipped out to Afghanistan, Sam is presumed dead when his Black Hawk helicopter is shot down in the mountains. At home in suburbia, the Cahill family suddenly faces a shocking void, and Tommy tries to fill in for his brother by assuming responsibility for himself, Grace, and the children.