This novel is a classic early 20th-century spy thriller that follows two British yachtsmen who stumble upon a German plot to invade England while on a sailing trip in the North Sea. The duo must use their wits and sailing skills to outmaneuver the Germans and alert the British government of the impending attack. The book is notable for its attention to detail and realism, particularly in its descriptions of sailing and the North Sea coastline.

In this adventurous tale, four young siblings find themselves unexpectedly cast out to sea when their planned sailing excursion in a borrowed boat takes a dramatic turn. Initially setting out for a simple exploration of the estuary, a thick fog and a series of mishaps lead them into the open waters of the North Sea. With no way to return and a sleeping pilot aboard, the children must muster all their courage and sailing knowledge to navigate the treacherous waters, facing the challenges of weather, navigation, and their own fears, as they endeavor to find their way safely back to shore. Their journey becomes not only a test of their physical abilities but a transformative experience that teaches them the value of resilience, responsibility, and the deep bonds of siblinghood.