Every summer, the Cazalet brothers - Hugh, Edward and Rupert - return to the family home in the heart of the Sussex countryside with their wives and children. There, they are joined by their parents and unmarried sister Rachel to enjoy two blissful months of picnics, games, and excursions to the coast. But despite the idyllic setting, nothing can be done to soothe the siblings' heartache: Hugh is haunted by the ravages of the Great War, Edward is torn between his wife and his latest infidelity, and Rupert is in turmoil over his inability to please his demanding wife. Meanwhile, Rachel risks losing her only chance at happiness because of her unflinching loyalty to the family.