Set in 1908, The Spy finds lead Van Dorn investigator Isaac Bell in the middle of an arms race as different nations try to update their navies using new technologies in guns, armor and propulsion (Robert K. Massie's 1992 Dreadnought details the real-world version of these efforts leading up to World War I). Germany and England eye each other as potential enemies, and each would like to enlist the United States on its side -- or at least ensure that the younger nation stays neutral. Across the Pacific, Japan is rapidly modernizing and would like to be certain that the U.S. is either no rival or at most one with a weakened and outdated Navy. So when three top engineers working on different aspects of the U.S. dreadnought battleship program die in accidents or suicides, there is no shortage of suspect nations once the coincidence is realized.
Into the mystery steps Bell, working as a private agent for a nation that has at the time a significant vacuum in its intelligence-gathering. Remember, in 1908 we have no FBI and no CIA. Intelligence falls to the members of the Secret Service, which also has to investigate crimes involving the Treasury Department and has recently added presidential protection to its duties. The Van Dorns and Isaac Bell are, naturally, the only ones who can probe the mystery and untangle the web of a mysterious spy who seems to be working for all parties at once to create as much chaos as he can manage.
The Isaac Bell books are part detective story, part suspense novel and part techno-thriller, even though they're set in the early 20th century. Much of Bell's work and success hinges on his ability to use the latest technology to his advantage, such as the Van Dorn's on-site photo lab where film taken by an agent in the morning can be seen as a printed picture the very same day. He also has a keen mind and is a man (naturally) of action, as capable with his fists as with his brain.
Cussler and Scott -- probably mostly Scott -- manage to layer on a flavor of an Edwardian adventure written at the time -- our heroes are stalwart, our heroines brave and beautiful, our villains nefarious and sneaky. Even though it's not an exact match, that atmosphere helps make The Spy a terrifically fun story to read as Isaac matches wits with his opponents, investigates the crimes and races across the country via his special Van Dorn railroad pass to try to catch up with the spy. It makes for a great vacation in the early 20th century and is a good reason to put future Isaac Bell stories on the book-buying list.