Two stories run side by side: the riddle of the title, concerning an unknown threat to England, and the redemption of a feckless civil servant named - naturally - Carruthers. The setting is lovely; the life aboard ship is vividly described; the author never leaves important details vague. 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.

Written in 1903, this is one of the greatest yachting adventure stories of all time. Additionally it is a darn good mystery. The story's charm comes from the interaction of two quintessentially English men who were once school chums -- the aristocratic Carruthers, who serves as narrator and secondary protagonist, and the shy, eccentric Davies, whose obsessive desire to check out a hunch sets them on an epic quest. The story's power comes from the North Sea, whose 12-foot tides and wild storms have carved out a unique marine landscape between the Friesian barrier islands and the Dutch and northern German coast. A silty body of mostly shallow water at high tide, a mostly walkable expanse ravine-scarred mudflats at low tide, and an astonishing spectacle of slow and fast-moving water when the tide is changing, this hybrid land- and seascape is, indeed, a riddle of the sands. The novel is a rich amalgam of intrigue and adventure, which opens the readers eyes to a landscape/seascape which few have seen. And it plays out against the gathering storm clouds of war. A fascinating nautical adventure full of mystery and intrigue.