DARK INVASION : 1915 : GERMANY'S SECRET WAR AND THE HUNT FOR THE FIRST TERRORIST CELL IN AMERICA
by Howard Blum

It is 1914 (three years before America entered World War I) and the United States is under attack. German saboteurs create these "accidents" where both munitions plants and cargo ships are exploding just about every day. To make things even crazier and just as scary, they throw in germ warfare.
New York Police Department Captain Tom Tunney is brought in to investigate. He is the head of the Bomb Squad and is determined to find these scoundrels and bring them to justice. Tunney assembles a group of detectives to hunt for the perpetrators. The more he digs, he realizes that this is not some small game but more intricate and dangerous than he expected.
Howard Blum has written a terrific book (it took him four years of research) that I actually did not want to end. It's riveting, exciting, and loaded with suspense. At the beginning of the book, Blum lists the cast of characters: the spies and the spycatchers. You think that you're not going to remember all of these names but as you get involved with the story, these people stick in your mind.
For those who love a good thriller that is a true story, you will definitely want to read Dark Invasion.
Very highly recommended.