The novel "owes a lot to the wonderful adventure novels of writers like Rider Haggard, that were a staple of Victorian Britain". It was a spy novel that "established a formula that included a mass of verifiable detail, which gave authenticity to the story – the same ploy that would be used so well by John Buchan, Ian Fleming, John le Carré and many others." All of the physical background is completely authentic - the various Frisian islands and towns named in the book actually exist and the descriptions of them accurate (often, from the author's own experience). The same is true for the various "sands" of the title - vast areas which are flooded at high tide but become mudflats at ebb. Navigating a small boat under these conditions requires a specialized kind of skilled seamanship - of which the character Davies is an unsurpassed master, and the descriptions of his feats are of abiding interest to yachting enthusiasts, quite apart from their role in the book's espionage plot.