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1. The Man of Mystery 2. A Secret Service Case 3. The High Flyers 4. The Mad Pursuit 5. Death Rides the Air 6. Another Visitor 7. On the Trail of “Mr. Seven” 8. A Sudden Attack 9. In the Valley 10. “Mr. Seven’s” Secret 11. Rescue from the Air 12. Against Time 13. Eastward Bound 14. The S-18 15. An Unknown Intruder 16.

The First Test 17. On the Bottom 18. The Missing Cook 19. The Warning Note 20. Isle of the Singing Trees 21. The Battle with the Iron Mate 22. Trapped 23. Desperate Hours

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