Book excerpt: This personal biography reveals the incredible true story of the British secret agent who posed as a Nazi spy during WWII. With Britain braced for a German invasion, MI5 recruited Walter Dicketts, a former officer of the Royal Naval Air Force—and a known con artist—as a double agent. Codenamed Celery, Dicketts was sent to Lisbon with the mission of persuading the Germans he was a traitor and then extracting crucial secrets. Once there, the Nazis brought Dicketts to Germany, where he had to outwit his interrogators in Hamburg and Berlin before returning to Britain as, in the Nazis’ eyes, a German spy. Even before he left for Germany, Celery knew that he had been betrayed by a fellow agent. Yet somehow he not only got back to Lisbon, but persuaded a German Intelligence Officer to defect before spending nine months undercover in Brazil. A mixture of hero and crook, Dicketts was smart, worldly and charismatic. Sometimes rich and sometimes poor, his private life was a complicated web of deception. Using both family and official documents, as well as police records, newspaper articles and personal memories, Carolinda Witt—Dicketts’s granddaughter—unravels the incredible yet true story of Double Agent Celery.