Boy Scouts in the North Sea; Or The Mystery of a Sub by G. Harvey Ralphson is an adventurous tale featuring a group of Boy Scouts navigating through a series of unexpected events during wartime. The story begins with the scouts led by Ned Nestor traveling from the German lines to a neutral port in Holland aiming to return to New York. Their journey takes a mysterious turn when a suspicious package marked U-13 is discovered in their luggage during a border inspection. The package disappears under mysterious circumstances leading to a series of encounters with a man named Mackinder who is determined to retrieve it. The scouts including Jimmie McGraw Jack Bosworth and Harry Stevens find themselves entangled in a web of espionage and danger as they attempt to secure passage back to the United States. Their efforts are thwarted by Mackinder who seems to have a personal vendetta against them. The narrative unfolds with the scouts' attempts to outwit Mackinder their interactions with Captain Johannes von Kluck and their determination to uncover the truth behind the U-13 package. The story is a blend of mystery adventure and the resilience of youth in the face of adversity.