Case of Agent 411, Classic Mystery and Adventure Book, Hudkins Publishing

This is a vintage classic mystery and adventure story. Bob Houston is a young clerk in the War Department. His uncle is a Department of Justice Agent. When some important radio secrets disappear, Bob helps his uncle recover them.

He proves himself so able that he is appointed as a provisional DOJ Agent. His adventures begin in earnest -- reaching a climax when he finds himself involved in bringing down an espionage ring.