Amid the chaos of the Great War, two elite assassins learn precisely how dangerous it is to have something—or someone—worth losing.

Ivy Olwen knows how to survive on the streets without two coins to rub together. Then destiny thrusts her into the nest of a covert agency of assassins sworn to drive back the world’s darkness, and she acquires a new set of lethal skills. Her education—from explosives to etiquette, sharpshooting to sabotage—is as far reaching as the organization’s missions. But it’s the hours she spends among the towering bookshelves in the library and stargazing on the roof with Agent Jack Vale that make her heart fly.

Jack knew plenty of hardship before the agency refined his rough edges, transforming him into the man who never misses. But he didn’t know the feeling of home until Ivy entered his world. Now Jack’s heart drums with a singular purpose: he will fight for her, fight alongside her. No matter the cost.

When the pair is sent on a seemingly simple mission to take down Russia’s newest and most dangerous arms dealer—a soulless man using the Great War as an opportunity to further his own depraved agenda—they discover that no amount of training could have prepared them for a manhunt that takes them across the frozen tundra, to the Crimean Peninsula, and along the Trans-Siberian Railway . . . only to discover that there is evil in the world they will never understand.