An unusually hot August in a rural area outside Pawhuska, Oklahoma. Beverly Weston, a once-noted, alcoholic poet, interviews and hires a young native American woman Johnna as a live-in cook and caregiver for his strong-willed and contentious wife Violet, who is suffering from mouth cancer and addicted to narcotics. Shortlly after this, he disappears from the house, and Violet calls her sister and daughters for support. Her sister Mattie Fae arrives with husband Charles Aiken. Her youngest daughter Ivy is single and the only one living locally; Barbara, her oldest, who has inherited her mother's strong will, arrives from Colorado with her husband Bill and 14-year-old daughter Jean. Barbara and Bill are separated and having marriage difficulties, but they put up a united front for Violet. Finally, middle daughter Karen arrives with the latest in a string of boyfriends, Steve Heidebrecht, a sleazy Florida businessman whom she introduces as her fiancé.
 

After five days, the sheriff shows up with the news that Beverly took his boat out on the lake and has drowned. Barbara identifies the body and makes the funeral arrangements. Mattie Fae's and Charles' shy, awkward son "Little Charles", misses the funeral because he overslept, and is met at the bus station by his father. Charles loves Little Charles, though Mattie constantly belittles her son's intelligence and calls him a loser. Ivy confides to Barbara that she is in love with Little Charles, and she cannot have children because she has had a hysterectomy.

The family sits down to an awkward dinner after the funeral, fueled by Violet's brutally honest "truth telling" which results in Barbara jumping on her mother. She decides she has had enough of the drug addiction, and confiscates all her pills. Later, after Violet has had a chance to sober up, she has a tender moment with her daughters, and reveals that her own mother had a cruel streak. Steve has been getting friendly with Jean and plying her with marijuana; Johnna catches him and goes after him with a shovel. Bill takes the car and goes back to Colorado with Jean; it is clear that he and Barbara are headed for divorce.

As Little Charles sings Ivy a song he has written for her, Mattie Fae walks in and berates him. This exhausts Charles' patience with his wife's lack of love and compassion for her son, and he angrily tells her he is taking Little Charles and leaving, with or without her. Mattie reveals to Barbara that she had an affair with Beverly, and Little Charles is in fact his son. Barbara promises to try to discourage Ivy from marrying Little Charles, while not revealing the secret. After the Aikens leave, Ivy tries to tell her mother about her love for Little Charles. Violet, who has hidden pills Barbara wasn't able to find, is high again and blurts out that she has known all along that he is Beverly's son. This drives Ivy to leave, angrily promising never to return. Barbara has finally had enough of her mother, and leaves in a pickup truck, leaving Violet alone with Johnna.