"Joe, come here!" Frank whispered.

"What is it, Frank?" asked his blond-haired brother. "I've heard that signal three times now, just as the clock struck midnight. Do you suppose it could be espionage? "

As the young detectives listened, the signal came again! The boys did not wait to hear more. They ran through the yard and pounced on the source. But there was nothing there! As the boys stood wondering, the call came again, from the other side of the lawn.

Suddenly Frank smacked his forehead. "We've been had, Joe. By a Northern Mockingbird, no less." His brother grinned sheepishly.

"I'm glad Dad wasn't here to see this!"

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