Cherie Priest's excellent Clockwork Century series, a steampunk saga set in the United States during a greatly extended Civil War, comes to a conclusion of sorts -- I mean, there is still plenty of room to explore in this world, if the author gets the urge -- in Fiddlehead, the most intense chapter of the series by far.

The American Civil War has dragged on for nearly 20 years, and the timeline has evolved accordingly even as technology has advanced at an exponential rate, driven by the needs of war. In this reality, Abraham Lincoln survived his assassination, although barely, and -- terribly deformed and crippled by the shot -- has resigned from the presidency and public life, although he still pulls some strings from his Washington, D.C., home and a mechanical chair that gives him some semblance of mobility. Ulysses Grant is in the midst of his third term as president, and even he -- once its greatest proponent -- is tired of the endless war.

Meanwhile, a massive computer, the eponymous Fiddlehead, has calculated the odds of victory, which appears unlikely to favor either the North or South as a far greater danger rises to put both sides at equal risk. Unfortunately, its inventor, a former slave, is hard pressed to persuade the public that its findings are real, and certain forces are at work to prevent him from spreading the word. On the other hand, a southern lady -- a wealthy capitalist who has found a way to weaponize (and monetize) the zombie plague that originated in the walled city of Seattle -- offers the Union a plausible end to the war ... although the finale might be grimmer than anyone is prepared to accept.

Assassins and turncoats, scientists and nurses and Pinkerton agents abound, and the zombie-like undead are spreading.

The story makes use of several characters from previous books in the series, in various minor and major roles. Priest also introduces several new ones ... not to mention bringing a few key figures from history, besides Lincoln and Grant, into the plot, all of whom are somewhat altered by differences in time and technology.

Fiddlehead is fast-paced and tense, with action, danger and thrills hurtling at the reader at breakneck speed. If you've ever wanted to see a pair of American presidents involved in a desperate nighttime gun battle with mercenaries, Mary Todd Lincoln wielding firearms in defense of her home, or dirigibles exchanging shots in the cold skies over Georgia, this is your book.

(It should be noted that the great computer that gave this book its title actually has very little to do with the plot and plays a very small role in the story. Honestly, I would have liked to see it used more, although that's my only criticism worth mentioning. The Clockwork Century are among the finest steampunk novels I've read, and I truly hope Priest revisits this world in the future.)