It is the most important day of young Frederick's life. Like a large number of children his age, Frederick is plagued by crippling anxiety brought on by a recent pandemic. He interviews for full time admittance into Kinth, a world renowned institute that is considered to be the only hope left for children like Frederick to live a normal life. Despite an apparent hallucination and a panic attack mid interview, Frederick is elated to find he has been accepted into Kinth. However, Frederick quickly learns that his admittance is conditional.

He, along with 19 other accepted applicants, will undergo further testing to determine whether or not they are truly Kinth material. Additionally, Frederick is informed that the applicants are discouraged from using their real names to avoid forming personal attachments, and will instead be called simply by their applicant numbers. Frederick, now Twenty, becomes fast friends with the picture perfect One, the ornery Seven and Thirteen, and the soft spoken Nineteen.

The odd nature of Kinth's testing convinces Frederick and his new friends that there is far more going on in Kinth than any of them first expected. Their suspicions are confirmed as they sneak from their dormitories to investigate the building and stumble across a dark room containing a shadowy beast that none of them remember seeing before, but have all had recurring nightmares of since childhood. Deeply shaken but equally determined, the group decides that the only way to remain at Kinth and uncover its secrets is to pass the unusual and rigorous testing. They strive to pass the tests and discover the truth that Kinth is so intent on hiding a truth that will change their lives forever.