In The Proof Ágota Kristóf continues the story of her earlier novel Le Grand Cahier (The Notebook). The country of the twin brothers Claus and Lucas is still at war. Claus crosses the border and leaves behind Lucas, who now remains alone in the house of their grandmother. Upon returning back home after his thirty-year-long absence, Claus finds that Lucas is gone. The lone survivor and only proof of their shared past is the ‘The Notebook’.