The Eldest Girl is a family drama spanning three generations. It moves between the 1960s with Tom, fresh off the boat from England who falls in love with the seemingly unattainable Ngahere, and 2010 where Cassius, their son, is grieving the death of his wife, Mere, and barely able to parent their children. When Mere's twin sister returns home a successful film producer and her troubled director husband leaves, she enlists Cassius's help with her three children. Tensions grow when Kiri, Cassius's daughter, becomes jealous and rebels, a daughter Tom never knew he had turns up, and the pressures of juggling a film project, a drunk husband and children increase. But when Tom has a heart attack and family secrets emerge, relationships are examined, and connections are retied.