Secret Agent K-7 Returns is a syndicated radio series that aired in 1939, featuring Agent K-7 and his fellow agents B-9, Z, and M, along with their assistants Rita Drake, Yvonne Durrell, and Patricia Norwood. The series consists of seventy-eight exciting and informative fifteen-minute spy stories set against the backdrop of rising tensions in Europe before World War II. In early episodes, K-7 would offer cautionary tales about spies undermining world peace, while later episodes saw him taking on a more active role and assisting his agents in capturing wrongdoers.

Each episode focuses on the agents' efforts to thwart various plans, such as sabotage, blackmail, assassination, and border violations. The stories present a mix of mystery, adventure, and suspense, and the female assistants often have their moments of bravery and resourcefulness. Notable for its historical relevance, the show subtly warns America about the dangers posed by Hitler's Germany and reflects the nation's war-weariness.

The sound quality of the series is excellent, and the episodes feature a blend of organ music and sound effects that evoke the atmosphere typical of old-time radio shows. Actor Walter Pigeon plays Agent Z in some episodes, but most of the voice actors remain unknown, much like the real-life spies they portrayed.