Agatha Christie. By Lucy Worsley. Pegasus Crime; 432 pages; $29.95. Hodder & Stoughton; £25 On December 3rd 1926 the famous novelist left her husband and young daughter and went missing for 11 days. That mysterious disappearance is at the heart of this colourful new biography, which pieces together what really happened that winter. A new, fascinating account of the life of Agatha Christie from c..