I. TRYING OUT THE NEW BIPLANE II. A RESCUER FROM THE SKIES III. THE MEN IN THE TOURING CAR IV. SUSPICION V. FIGURING IT ALL OUT VI. AN UNKNOWN ENEMY VII. SEEN FROM THE EAGLES' EYRIE VIII. MYSTERIOUS MR. MARSH AT IT AGAIN IX. STARTLING NEWS OVER THE WIRE X. IN PARTNERSHIP WITH THE CHIEF XI. A NEW ALARM XII. SANDY DROPS SOMETHING XIII. THE CHALLENGE XIV. SOMETHING DOING XV. THE AWAKENING XVI. THE CHIEF MEETS AN OLD FRIEND XVII. GALLANT ANDY XVIII. AT THE FOOT OF THE LIBERTY POLE XIX. THE MYSTERY STILL UNSOLVED XX. THE RIVAL AVIATORS XXI. THE RACE WITH THE STORM XXII. A TERRIBLE MOMENT ON OLD THUNDER TOP XXIII. THE BIRD BOYS' TRIUMPH—CONCLUSION