On 20 May 1940, as Hitler's tanks reached the French coast, Churchill sent a secret message to Roosevelt, begging for US help. On the same day, MI5 forced its way into the London flat of Tyler Kent, a code clerk at the US embassy. They found 1929 stolen messages, including that morning's desperate plea. Kent's trial and arrest for espionage was unprecedented in the period. But was he really a spy? And if so, for whom? Using documents and reports never previously published, the authors piece together the story of Tyler Kent's treachery. Anthony Read is co-author of "Kristallnacht" which won the Wingate Literary Award.