CONTENTS

ChapterPage
I—A Package Vanishes[7]
II—Difficulties and Danger[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 “U-13”

CHAPTER I
A PACKAGE VANISHES

“Good night!” exclaimed a lad of about eighteen peering from the window in a railway coach. “This train’s running on a regular lake!”