"At the end of The Golden Specific, Sophia was on her way home to Boston, anticipating her reunion with Theo. But he has been conscripted to fight in the Western War—Prime Minister Broadgirdle’s twisted vision of Manifest Destiny. Shadrack is in his thrall as War Cartologer and cannot help his niece.
Sophia leaves right away to track down her best friend and solve the mystery of her parents once and for all. Then Shadrack hears of a horrifying weapon. It is a red fog called the Crimson Skew, and if you inhale it, you become a murderer. Sophia and her companions—and Theo’s army company—are directly in its path. There is a fate worse than death, and it is about to ruin their lives… "
Series was wrapped up nicely, though there were a few miscellaneous questions that I found annoying that weren't answered. There also seems to be an opening for another book in this series, though it's branded as a trilogy. All in all, a great series that I was thoroughly engrossed in and consumed in a matter of days.