On the evening of 3 December 1926, Agatha Christie left her home in Sunningdale, Berkshire, in her Morris Cowley. The next morning, the car was found abandoned, balanced precariously on the edge of a quarry. Ten days later, Agatha was discovered in a hotel in Harrogate, claiming to have lost her memory. Lucy Worsley delves into this traumatic watershed moment in Agatha's life.