Contents

CHAPTERPAGE
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”