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| Chapter I—Green Hat, the Trouble-starter | [11] |
Dave Darrin and Dan Dalzell, while ashore at Gibraltar, have an exciting experience with a spy and stir up a deep mystery. |
| Chapter II—Dan's Thirty-three-dollar Guess | [27] |
Admiral Timworth solves the mystery for the ensigns and amazes them very much. |
| Chapter III—The Startler at Monte Carlo | [43] |
Danny turns a trick on a brother officer. Ashore at Monte Carlo the young ensigns find the makings of future trouble. |
| Chapter IV—Mr. Green Hat's New Rôle | [55] |
Dave loses a human trail and saves a human life. Then the plot begins to thicken. |
| Chapter V—Danny Grin Fights a Smile | [70] |
Mr. Green Hat sets a trap at the gambling resort, into which Ensign Dalzell smilingly walks. |
| Chapter VI—Dave Runs into a Real Thrill | [78] |
A desperate plot to involve his country heard by Dave Darrin, who acts swiftly on the information he has obtained. |
| Chapter VII—The Admiral Unloads His Mind | [87] |
Called before the Admiral, the young officers make their report. The former sends a wireless to Washington, later summoning the ensigns to his quarters for secret orders. |
| Chapter VIII—On Lively Special Duty | [96] |
A delicate international situation is explained to Dave and Danny, who are then ordered ashore at Naples on a special and perilous mission. |
| Chapter IX—M. Dalny Plans a Tragedy | [102] |
Darrin meets one of the men he is looking for. As a result of that meeting he and Dan are sentenced to death. |
| Chapter X—Treachery has the Floor | [116] |
Enticed away for a drive, the Naval officers find themselves in a disreputable section of Naples and on the threshold of a tragedy. |
| Chapter XI—Hemmed in by the Bravos | [124] |
Dave and Dan are attacked by a mob of Sicilian bravos and fight a desperate battle to save their own lives. |
| Chapter XII—Evil Eyes on Sailorman Runkle | [132] |
The young officers now discover the real reason for the attempt on their lives, but, though they do not know it, fresh perils await them. |
| Chapter XIII—Orders Change in a Minute | [138] |
Able Seaman Runkle, bearing an important communication from Darrin to the Captain of the U. S. S. "Hudson," gets into serious difficulties. |
| Chapter XIV—Dan has very "Cold Feet" | [151] |
Beset by spies, the two young officers set out on a long journey after an exciting start, later finding that they have been guilty of a grave oversight. |
| Chapter XV—At the American Embassy | [161] |
Dave and Danny arrive in Paris, where they are the guests of the American Ambassador. Darrin trails an international plotter and makes an important discovery. |
| Chapter XVI—"Seeing" the Paris Apaches | [179] |
The young ensign, after picking up a valuable clew, is attacked by savage Paris Apaches, who, angered by his defense, determine to take his life. |
| Chapter XVII—Dave's Guess at the Big Plot | [189] |
The details of a plan to involve the United States in war with England are unfolded to his Admiral by Ensign Dave. |
| Chapter XVIII—Surigny's Next Move | [198] |
English and American officers join hands and one gets a remarkable message from an international plotter as the trail grows hot. |
| Chapter XIX—Truth, or French Romance | [207] |
Dave meets an acquaintance and listens to an astounding confession. |
| Chapter XX—The Allies Clear for Action | [213] |
"A submarine will sink the British battleship to-night," is the startling information imparted by Dave to his companions. |
| Chapter XXI—Making Stern Work of It | [223] |
The young American Naval officer in command of a boarding party on the plotter's yacht, is neatly trapped. |
| Chapter XXII—After the Pest of the Seas | [233] |
Ensign Darrin and his crew on the Navy launch make an exciting discovery after accomplishing a brilliant capture. |
| Chapter XXIII—The Puzzle of the Deep | [240] |
While engaged in a thrilling chase after an undersea boat the launch's company find the tables unexpectedly turned on them. |
| Chapter XXIV—Conclusion | [249] |
The pursuit comes to a stirring finish, with Able Seaman Runkle's reputation saved and Ensign Darrin highly honored. |
