Christine Lucas is the main character in the novel "Before I Go to Sleep" by S.J. Watson. She is a woman in her forties who suffers from amnesia, losing her memory every time she falls asleep. This condition makes it difficult for her to piece together her past and understand her present life. Throughout the story, Christine relies on her husband, Ben, and a journal she keeps to help her remember important details about herself and her relationships. The novel explores themes of memory, identity, and trust, as Christine navigates her daily challenges and seeks to uncover the truth about her life.