Contents
| CHAPTER | PAGE | |
| I | A Package Vanishes | [7] |
| II | Difficulties And Dangers | [18] |
| III | The Man With The Scar | [30] |
| IV | the Lena Knobloch | [42] |
| V | Two Mysterious Changes | [54] |
| VI | A Difficult Departure | [65] |
| VII | A Warning From The Sea | [76] |
| VIII | More About The “U-13” | [87] |
| IX | A Strange Visit | [98] |
| X | Shipwreck And Rescue | [109] |
| XI | A Fleet Of Submarines | [120] |
| XII | A New “U-13” Appears | [131] |
| XIII | A Threatening Situation | [142] |
| XIV | Helped By An Enemy | [153] |
| XV | Mistaken Identity | [165] |
| XVI | A Strange Discovery | [176] |
| XVII | Alone And Helpless | [187] |
| XVIII | Help From A Stranger | [198] |
| XIX | Mackinder Again | [209] |
| XX | A Mysterious Craft | [221] |
| XXI | A Mystery Explained | [232] |
| XXII | More Mystery | [240] |
| XXIII | The Mystery Of The “U-13” | [246] |
Boy Scouts in the North Sea;
or,
“The Mystery of a Sub”