Christmas Day 1944: After his last mission put him in the tailspin of the Battle of the Bulge, Captain Billy Boyle travels to southeast England to visit his girlfriend, Diana Seaton, for a brief holiday respite. Diana is engaged in classified work at RAF Hawkinge, including Operation Corona, which recruits German-speaking Women's Auxiliary Air Force members - many of them Jewish refugees from the Kindertransport rescue - to countermand German orders and direct night fighters away from Allied bombers. It's fascinating and critical espionage work, but it's laced with peril, as Billy finds out. On a scenic Christmas walk along the White Cliffs of Dover, Billy and Diana stumble upon the dead body of a US Air Force officer. In the dead man's pocket are papers with highly confidential information about radio interception operations. Information worth killing over. As Billy digs into the secret world of codebreakers and radio jammers stationed at Hawkinge, another body turns up. Now Billy must find out what connects these two men - and who was so hell-bent on silencing them. Enlisting the help of his long-time associates, Billy undertakes another thrilling investigation that brings him to war-torn Yugoslavia, where he must rescue an escaped POW who may be the only person who knows the truth.