In 1963 Montana, retired sheriff George Blackledge and his wife Margaret, live with their son, James, his spouse, Lorna, and their newborn grandson, Jimmy. James is killed when he is thrown from a horse, breaking his neck.
Three years later, Lorna marries Donnie Weboy, though it is made obvious during the dour nuptials that the wedding is one of necessity. While out one day, Margaret happens to observe Donnie physically abusing both his wife and now 3-year-old Jimmy. Margaret decides to check in with Lorna and Jimmy at their new home. Shortly afterwards, Donnie leaves town with Lorna and Jimmy, causing Margaret to worry over Jimmy’s safety. She eventually convinces George that the situation is dire enough to intervene, and the two set off to find the family.
Various sources clue them into the whereabouts of the Weboy family, until finally Margaret and George locate Donnie’s uncle, Bill Weboy. Their initial meeting is cold, but Margaret refuses to be intimidated and accepts Bill’s invitation to the Weboy’s homestead for dinner. At dinner, they meet Donnie’s family, including Blanche, Donnie’s intimidating and disturbing mother. Her charms do not last long as the dinner conversation progresses and an attempt from Margaret to carry Jimmy out of the house turns sour.
George and Margaret find themselves at odds with the Weboys, and a conflict grows when the grandparents attempt to sneak Lorna and Jimmy out of the abusive living environment. Blanche will stop at nothing to keep Lorna and Jimmy under her control and her sons and brother facilitating and perpetuating her manipulation. George gets shot and killed by Blanche in an intense fight in the Weboy home, but not before helping Lorna and Jimmy flee the flaming ruins of the home. As he is dying, Margaret aims and fires a shotgun at Blanche, killing her immediately. Margaret tearfully bids goodbye to her husband, and with the entire Weboy family now engulfed in flames and no longer able to harm them, takes Lorna and Jimmy back to Montana with her where they are finally safe.