Normal seventeen-year-old girls go to high school, binge watch TV shows all weekend, and flirt with everyone on the face of the Earth. But Ryn Whitaker is trying to save it. Ryn is a Citadel. A soldier. A liar. Ryn and her fellow Citadels were specially chosen and trained to guard a Rift--one of fourteen unpredictable tears in the fabric of the universe that serve as doorways to alternate Earths. Unbeknownst to her family, Ryn leaves for school each day and then reports for duty as an elite, cybernetically-altered soldier who can run faster, jump farther, and fight better than a Navy SEAL--which comes in handy when she's not sure if axe-wielding Vikings or any number of other scared and often dangerous beings come through the Rift. A fine-tuned weapon, Ryn is a picture-perfect Citadel. But that's all about to change. When a young man named Ezra is pulled through the Rift, Ryn finds herself immediately drawn to him, despite her training. What starts as a physical attraction quickly grows deeper, and Ezra's curiosity throws Ryn off balance when he starts questioning the Rifts, the mysterious organization that oversees them, and the Citadels themselves--questions that lead Ryn to wonder if the lies she's been telling her family are just the surface of a much bigger lie told to her. As Ryn and Ezra desperately try to get to that truth, they discover that each revelation blurs the line between the villains and the heroes even more.