Fiddlehead

"Young ex-slave Gideon Bardsley is a brilliant inventor, but the job is less glamorous than one might think, especially since the assassination attempts started. Worse yet, they're trying to destroy his greatest achievement: a calculating engine called Fiddlehead, which provides undeniable proof of something awful enough to destroy the world. Both man and machine are at risk from forces conspiring to keep the Civil War going and the money flowing. Bardsley has no choice but to ask his patron, former president Abraham Lincoln, for help. Lincoln retired from leading the country after an attempt…