A sealed room. A murdered psychiatrist. A decades-old secret someone will kill to protect.When Dr. Marcus Holloway is found dead inside his locked office—surrounded by disturbing patient files from a long-buried experimental program—Captain Kate Gazzara is pulled into her most dangerous investigation yet. Someone is hunting down the survivors of a secret psychiatric trial gone horribly wrong.Armed with surgical precision, digital surveillance, and a motive rooted in trauma, the killer is always one step ahead. The files name 47 patients. Now they’re dying one by one.Who is Subject 23? And how do you catch a killer who already knows you’re coming?