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A Nutty Solution

Where would you hide a cipher sheet? A Soviet agent, operating in West Berlin in the 1980s, had a cunning idea: stash it in an empty walnut shell in a bowl of nuts. But the agent made one mistake.
The agent sealed the shell with glue that glowed in ultraviolet light. West German police, searching the apartment with a UV light, examined each nut. One glowed.
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