Roubaix, December 2006. Junon Vuillard, married to Abel, is the iron-willed matriarch of the family. Junon held her family together through tough times, but her willpower made her children resentful. She remains handsome, and though her husband is obese and elderly, he retains clarity, acceptance, tolerance, and unconditional love for his family. He and their mutual love holds a fragmented family together, albeit uneasily.
They have three children in their 30s. The eldest is Elizabeth, a successful playwright married to the equally successful Claude. Their only child, 16-year-old Paul, is mentally ill and takes strong medication. The middle child is Henri, who drinks too much and has always fought with everyone else. He has a new girlfriend, Faunia. Ivan is the youngest sibling, married to Sylvia with two sons, Basile and Baptiste. Henri and Ivan are friends with Simon, a cousin who was raised with them after his parents' death. Simon works in Abel's plant, but is a part-time artist. He is an alcoholic, frequently in trouble for public brawling. All three men were interested in Sylvia once, but manipulated her to think that only Ivan loved her; she married and grew to love him. A deceased sibling, Joseph, is the presence around which everyone's psyches revolve: he died of leukemia at age six, after his parents tried to save him by having another child who might be a bone marrow donor.
Six years before the family's latest Christmas gathering, Henri faced bankruptcy. Elizabeth paid off his debts, but demanded that he never see her again, meaning he had to be excluded from family gatherings. Family members speculate on the reason Elizabeth set this condition.
Just before Christmas, Junon learns she has acute myeloid leukemia and will soon die unless she undergoes a bone marrow transplant. Her extended family gathers at her home and immediately start bickering. Junon has asked them to be tested to see if they qualify to donate their bone marrow. Elizabeth fights with Henri, who drinks heavily and hides Paul's medication. Paul fears the blood test might reveal Claude is not his biological father. Henri refuses the test, because he never loved his mother. Faunia has agreed to visit before leaving to spend the holiday with her own family. Her honesty and gentleness soothe Henri, and she stays for two days.
On 23 December, Rosaimée visits for dinner and fireworks. She was Abel's mother's friend, although it is suggested that they were lesbian lovers. Rosaimée tells Sylvia that Simon stopped seeing Sylvia because he believed she would be happier with Ivan. Sylvia feels betrayed and manipulated. Henri is tested, discovers he qualifies as a donor, and decides he wants to. Simon begins drinking heavily in cafes, and the family searches for him. Sylvia finds him and confesses that she knows he loves her. She and Simon spend several hours talking, then return to the house and have sex. Paul tells Henri about his fears. Henri convinces him that he is not his father, confirmed by the test, and reassures Paul that it is not a failing to be afraid. They bond, and Paul's mental condition improves. On Christmas Day, Abel and Elizabeth discuss Elizabeth's longstanding depression, and Abel reads her the prologue to Friedrich Nietzsche's On the Genealogy of Morality, which discusses how well people know or do not know themselves. Abel suggests that Elizabeth fears death, and this has led to her caution and depression.
Ivan discovers Sylvia has had sex with Simon. They made no effort to hide it, waking up together in bed and greeting her children as they come bearing tea. Ivan seems hardly to respond, as though he has expected it. Paul stays behind with Henri, who is having a positive effect on his mental health. Henri donates his bone marrow to Junon, but she announces her conviction that her body will reject the transplant. Elizabeth speculates that Junon will live, while Henri flips a coin in the hospital in front of his mother, but does not reveal the result.
