The story is narrated by an English gentleman Currthuers, who received an unexpected invitation of duck shooting from an old friend Davies. Being tired of his neglected position in society, he accepts it to go to the North Sea only to find that he is involved in a mystery, or the riddle of the Sands. His friend claims theres something in the air, something hiding behind the misty coast of Germany. But how can they prove it?
As a story, The Riddle of the Sands is far from perfect. It is full of authentic descriptions of local landscapes (the author actually cruised his yacht there), but at the same time frequent reference to the geographical data and nautical terms are a bit wearisome to readers, and moreover, the narrator often refers us to the maps in the appendix. Those things only slow down the action of the novel, and actually the book sometimes has to go through lull.
But, wait a while. The story gets gradually faster, and as the adventure of the heroes slowly gets near to the core of the plot, the tale becomes more and more gripping. Though characters sometimes are just more than cardboard (and especially female part is poorly done), your patience will be rewarded.
It is well-known that Sherlock Holmes in His Last Bow turns a spy for his country, and says Theres an east wind coming. The meaning of what Holmes says is clear to the comtemporary people, and Childers, a politician, also wrote his book not as an amusement but as a warning to England about the coming threat of Germany, and actually The Riddles of the Sands was written about 10 years before WW1 began. In this historical context too, the book is interesting, and the tediousness of the opening chapters is justified if you keep it in mind that it is meant for Childerss sarcasm against indifference and complacency among the English people (talking of English complacency, we remember later in 1938, immediately before WW2, Alfred Hitchcock again uses it as a satire in his thriller The Lady Vanishes with brilliantly silly two British gentlemen who are more concerned with cricket games than surrounding danger). People dont change.
So, the book itself is still enjoyable, but these historical matters will make it more precious; after all, it is one of the proof how people reacted to the coming change in the history of mankind.