Charlie Saxe grew up in the seedy underbelly of Umbra before she was adopted and allowed to live in the palace. Since then, she has been training for years to be able to infiltrate an Equivalent high school, a task she needs to succeed at in order to make her adoptive father proud. Everyone in her world knows about the existence of the parallel universe Equivalent, but only trained soldiers are allowed to go there. After all her hard work, she refuses to let anything get in her way, including the inappropriate crush she happens to have on her target, Kav Kavanaugh.

However, when the only thing she can do to keep him safe is illegally sneak him in to her world, Charlie is forced to put her personal needs aside. Counterpart is run by a monarchy, and she and Kav must help her King uncover a mole within the palace before Kav can return home. As the two of them grow closer, Charlie makes contact with the boy she left behind in Umbra, and discovers a conspiracy theory against the king that could change everything she thought she knew and believed in.