Rodolphe Marcnoi's The Last Day concerns the troubled history of a family. Eighteen-year-old Simon (Gaspard Ulliel) meets the attractive 17-year-old Louise (Melanie Laurent) while he travels on a train to spend Christmas with his family. She joins him onhis visit home. Simon's mother, Marie (Nicole Garcia), is happy to see her son, but dad (Christophe Malavoy) loves to complain and harass his family, and sister Alice (Alysson Paradis) competes fiercely with her brother. The family mistakenly believes that Simon and Louise are intimately involved with each other. Eventually, their interactions reveal buried truths about various members of the family.