That Sweet Little Old Lady

Usually, the toughest part of the job is stating the problem clearly, and the solution is then easy. This time the FBI could state the problem easily; solving it, though was not. How do you catch a telepathic spy?

In 1914, it was enemy aliens.
In 1930, it was Wobblies.
In 1957, it was fellow travelers.
And, in 1971....