RAY: David Thorndike had been operating as a spy, behind the German lines. As the son of an English father and a German mother, he was perfectly suited for the job. His knowledge of the language, German culture, music and history were unsurpassed.

And yet he was not above suspicion. He was watched carefully, but never a false move did he make. As the war wore on and invasion plans materialized, he became encouraged, even euphoric, that soon the war would end and he would return to jolly old England.

Then one day he was in Berlin, lost in his thoughts, thinking about his return to merry old England. He was standing there on a busy street corner, ready to cross the street, and he feels a tug on his sleeve and a pistol in his ribs. He's been discovered.

How did they know?!

[ Car Talk Puzzler ]