Le Queux, William T.: The Czar's Spy: The Mystery of a Silent Love. v1, 19 Jan 2008
 

From Wikipedia:

William Tufnell Le Queux (July 2, 1864 London - October 13, 1927) was a British journalist and writer. He was also a diplomat (honorary consul for San Marino), a traveller (in Europe, the Balkans and North Africa), a flying buff who officiated at the first British air meeting at Doncaster in 1909, and a wireless pioneer who broadcast music from his own station long before radio was generally available; his claims regarding his own abilities and exploits, however, were usually exaggerated.

He wrote in the genres of mystery, thriller, and espionage, particularly in the years leading up to World War I, when his partnership with British publishing magnate Lord Northcliffe led to the serialised publication and intensive publicising (including actors dressed as German soldiers walking along Regent Street) of pulp-fiction spy stories such as The Invasion of 1910, The Poisoned Bullet, and Spies of the Kaiser. These works were examples of invasion literature, a common phenomenon in pre-WWI Europe involving fictionalised stories of possible invasion or infiltration by foreign powers; Le Queux's specialty, much appreciated by Northcliffe, was the German invasion of Britain. He was also the original editor of Northcliffe's War of the Nations.

The Czar's Spy: The Mystery of a Silent Love is considered by some to be the greatest spy novel of all time.