They left a note at the crime scene addressed to Special Agent Kira Cross.

Save what you can, but look next week if you can. Tik-Tok.

Fifty-one million dollars in luxury watches stolen by remote-controlled drones — no suspects, no physical evidence, no footprints, just a promise that something worse is coming.

Each week brings a new protocol, each one more audacious than the last. A young woman kidnapped without a single human being setting foot near her. A serial killer cold case spanning thirty years and sixty-seven victims. A twenty-year-old Harvard exchange student, buried alive in a sealed coffin somewhere beneath the city, with seven days of air and a set of cryptic clues standing between her and death.

Each protocol involves solving clues within a strict timeframe — if one clue is left unsolved, people die. Kira and her team are put to the absolute test. Tik-Tok.

The criminal architects have been playing this game for decades. Now they are playing it with Kira Cross.

When she steps into an autonomous taxi that doesn't stop, that jams her phone and accelerates onto an empty highway, Kira Cross becomes the Fifth Protocol.

The truth doesn't hide in the shadows. It doesn't hide in plain sight. It hides in the Darkdown.